# Pitch size and diameter of bolt **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [July 21, 2017, 2:45pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108 "2017-07-21T14:45:53Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![mattwilliamd34](https://avatars.discourse-cdn.com/v4/letter/m/ac91a4/32.png) [@mattwilliamd34](https://community.cartalk.com/u/mattwilliamd34)\ **Post date:** [July 21, 2017, 2:45pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/1 "2017-07-21T14:45:53Z")
This has got nothing to do with cross threading but want to gain abit of knowledge of bolts in general as this will help in the future . If the female thread ( not nut ) is interrogated into the engine it self or any other place around the engine bay does it have to be the same diameter length wise and pitch size as the male thread in order for it to engage into the male threads. Like for example M8x1.25 does the female thread have to be that size . Some people have been really helpful on here and really do appreciate the help ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [July 21, 2017, 3:03pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/2 "2017-07-21T15:03:34Z")
Here you go. Bet you thought threads were simple, huh? šŸ˜ > **[ISO metric screw thread](https://en.wikipedia.org/wiki/ISO_metric_screw_thread)** > > The ISO metric screw threads are the worldwide most commonly used type of general-purpose screw thread. They were one of the first international standards agreed when the International Organization for Standardization (ISO) was set up in 1947.\[citation needed\] > The "M" designation for metric screws indicates the nominal outer diameter of the screw, in millimeters (e.g., an M6 screw has a nominal outer diameter of 6 millimeters). > The design principles of ISO general-purpose metric screw threads (... ---
**Author:** ![mattwilliamd34](https://avatars.discourse-cdn.com/v4/letter/m/ac91a4/32.png) [@mattwilliamd34](https://community.cartalk.com/u/mattwilliamd34)\ **Post date:** [July 21, 2017, 3:25pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/3 "2017-07-21T15:25:42Z")
Yeah quite allot of information but does the thread size e.g major diameter have to be the same size as the female internal thread that is integrated into the engine and the same pitch size. Didnt seem to explain on that website you gave me ---
**Author:** ![BillRussell](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/billrussell/32/3179_2.png) [@BillRussell](https://community.cartalk.com/u/BillRussell)\ **Post date:** [July 21, 2017, 3:27pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/4 "2017-07-21T15:27:49Z")
Because that is taken for granted. A 6-32 nut works with a 6-32 screw only. ---
**Author:** ![sgtrock21](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/sgtrock21/32/246_2.png) [@sgtrock21](https://community.cartalk.com/u/sgtrock21)\ **Post date:** [July 21, 2017, 3:30pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/5 "2017-07-21T15:30:54Z")
Thank you Bill for saving me the trouble of stating the obvious. ---
**Author:** ![mattwilliamd34](https://avatars.discourse-cdn.com/v4/letter/m/ac91a4/32.png) [@mattwilliamd34](https://community.cartalk.com/u/mattwilliamd34)\ **Post date:** [July 21, 2017, 3:40pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/6 "2017-07-21T15:40:02Z")
Im talking metric though not inches ---
**Author:** ![jdmere](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/jdmere/32/3002_2.png) [@jdmere](https://community.cartalk.com/u/jdmere)\ **Post date:** [July 21, 2017, 4:13pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/7 "2017-07-21T16:13:35Z")
Doesnā€™t matter. They have to be the same size. ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [July 21, 2017, 5:45pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/8 "2017-07-21T17:45:54Z")
> [@mattwilliamd34](#): > > M8x1.25 does the female thread have to be that size Absolutely. The length is a different issue. If there is a blind tapped (threaded but only to a certain depth) hole in a block you should use the same length bolt or less in that hole. If you donā€™t, you can screw it in far enough that it bottoms before the part you are trying to attach is tight or it breaks out the backside of that blind hole. And really bad things can occur if that happens. ---
**Author:** ![sgtrock21](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/sgtrock21/32/246_2.png) [@sgtrock21](https://community.cartalk.com/u/sgtrock21)\ **Post date:** [July 21, 2017, 6:04pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/9 "2017-07-21T18:04:49Z")
Iā€™m fairly confident 6mm is metric. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [July 21, 2017, 6:49pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/10 "2017-07-21T18:49:09Z")
> [@mattwilliamd34](#): > > the thread size e.g major diameter have to be the same size as the female internal thread that is integrated into the engine and the same pitch size. Yup. The same applies to metrics as to inches. Thereā€™s a book called ā€œThe Machinistsā€™ Handbookā€ that goes into great depth on threads. It isnā€™t inexpensive, but if you really want to know in-depth about threads, I recommend it. Itā€™s the ā€œbibleā€ when it comes to threads. ---
**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\ **Post date:** [July 21, 2017, 8:27pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/11 "2017-07-21T20:27:34Z")
> [@mattwilliamd34](#): > > This has got nothing to do with cross threading but want to gain abit of knowledge of bolts in general as this will help in the future . > If the female thread ( not nut ) is interrogated into the engine it self or any other place around the engine bay does it have to be the same diameter length wise and pitch size as the male thread in order for it to engage into the male threads. Like for example M8x1.25 does the female thread have to be that size . YES, to answer your question. For a little more insightā€¦ Metric threaded fasteners, use a format like _M8x1.25mm_ to indicate that the screw/bolt (or hole that it fits) is 8 millimeters in diameter and has a thread ā€œpitchā€ of 1.25 millimeters, meaning that each thread is 1.25mm apart from the adjacent threads. What is left out of the M8x1.25 screw/bolt dimension is the length of the fastener. An M8x1.25x 25mm _length_ would have 20 threads (count them!), from head to end (25mm _divided by_ 1.25mm). An M10x1.5 x 30mm (length) fastener would also have 20 threads. Although it is longer, the thread pitch is coarser (distance between threads is greater). Not to confuse the issueā€¦ Inch size fasteners (non-metric), like 3/8-16 use a little _different method for designating thread pitch_. So, a 3/8" (diameter) bolt with a thread pitch of 16, has 16 threads per inch (rater than a distance between threads). A _3/8-16_ x 2" length bolt would have 32 threads from head to end (16 x 2"). Have you used a metric ruler very much? Pick up a metric ruler or tape measure and get to know it a bit if you havenā€™t done so. Try it out! measure how long an 8Mx1.25 bolt is and divide that length by 1.25. Then count the threads. The number should match your math. _ **CSA** _ ---
**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\ **Post date:** [July 21, 2017, 10:23pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/12 "2017-07-21T22:23:27Z")
Iā€™ve seen a number of people mate different thread fasteners togetherā€¦ Breaking them off or getting them out later is a different issue altogether. A neighbor of mine came over one evening and was having trouble stabbing a manual trans back into his truck after a clutch job. Of course he did not know the clutch disc had to be aligned so he offered me 40 bucks just to stab it. Once stabbed, Iā€™m looking around in the debris on the floor for the two 10 MM nuts that fit onto the lower studs mating the trans to engine block. He says he has them. He crawls back under the truck with what is obviously two 3/8 NC Grade 2 fence post nuts and starts pounding them onto the studs with a hammer. I asked him what he was going to do if they had to come back off. ā€œProbably wonā€™t have toā€¦ā€ and at that point I bailed out. ---
**Author:** ![Yosemite](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/yosemite/32/643_2.png) [@Yosemite](https://community.cartalk.com/u/Yosemite)\ **Post date:** [July 21, 2017, 10:32pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/13 "2017-07-21T22:32:11Z")
That is funny but sad @ok4450 . I once saw a farmer hanging a small shed door. He told me that he couldnā€™t keep the hinges on the frame. At that point I witnessed him drive the screws as if they were nails. Yosemite ---
**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\ **Post date:** [July 21, 2017, 11:04pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/14 "2017-07-21T23:04:04Z")
> [@ok4450](#): > > He crawls back under the truck with what is obviously two 3/8 NC Grade 2 fence post nuts and starts pounding them onto the studs with a hammer. > I asked him what he was going to do if they had to come back off. ā€œProbably wonā€™t have toā€¦ā€ and at that point I bailed out. One of the times I worked at a Volkswagen dealer, we had a strange assortment of ā€œmechanics.ā€ We had a hippy (with a large ā€œPEACEā€ painted on it) Volkswagen type 2, guys who ā€œmoon-lightedā€ as ā€œmechanicsā€ (one guyā€™s OTR truck diver uncle), a fire-arms dealer, and one ā€œmechanic,ā€ Moose, who didnā€™t own any metric tools! When heā€™d get in a ā€œtight spot,ā€ heā€™d yell to see if he could borrow a metric wrench from a neighbor. They all had nicknamesā€¦ Happy Apple, Johnny O, Yugi, etcetera. The guy named ā€œSuds,ā€ no joke, would say, _ā€œA good cross-thread is better than a lock-washer!ā€_ Given this place and people, I never really knew whether he was joking or not. When getting parts for customer cars, heā€™d almost always say (for parts under about 5 bucks), _ā€œYouā€™d better give me 2! I always screw the first one up!ā€_ His customers were charged. I actually think he was just supplying his toolbox for week-end work at home (I hope). _ **CSA** _ ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [July 22, 2017, 12:08am UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/15 "2017-07-22T00:08:03Z")
The ā€œsizeā€ of a bolt is its diameter measured on the threaded portion. The hole diameter has to match up to that, but be a little bit larger obviously. See a tap size vs hole diameter table for info about that. Sometimes confusion develops about which socket (or wrench) size corresponds to the bolt size. The corresponding socket size is usually larger than the bolt size, b/c the socket fits on the head of the bolt which has a larger diameter. A one inch bolt requires a larger than one inch socket in other words. The other things you have to worry about being fit-compatible is the thread pitch, metric M8-1.25 vs an inch size like 3/8-16, and you need a bolt of the proper length for the application of course. Bolts and nuts are made in different materials, different coatings, and different strengths too. ---
**Author:** ![CapriRacer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/capriracer/32/22_2.png) [@CapriRacer](https://community.cartalk.com/u/CapriRacer)\ **Post date:** [July 22, 2017, 9:25am UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/16 "2017-07-22T09:25:15Z")
I see no one has talked about - and Iā€™m searching for the correct word and I think it is - ā€œClass of Fitā€. There are several different classes of fit for thread fasteners - from loose (where the nut is quite a bit larger than the bolt) to interference (where the nut is actually smaller than the bolt) These are standardized and labeled and every bolt and nut should have a class identified - although I understand that ā€œNormalā€ is usually not specifically identified. [https://www.fastenal.com/content/feds/pdf/Article%20-%20Screw%20Threads%20Design.pdf](https://www.fastenal.com/content/feds/pdf/Article%20-%20Screw%20Threads%20Design.pdf) ---
**Author:** ![mattwilliamd34](https://avatars.discourse-cdn.com/v4/letter/m/ac91a4/32.png) [@mattwilliamd34](https://community.cartalk.com/u/mattwilliamd34)\ **Post date:** [July 22, 2017, 1:42pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/17 "2017-07-22T13:42:00Z")
Thankyou for all the information , now I know a little bit more , it does makes sense that the pitch size and major diameter has to be the same size in major diameter and pitch size for the female ((internal thread) just wanted reassurance in the end and a little bit more Informatioun . Cheers for the advice thankyou . ---
**Author:** ![mattwilliamd34](https://avatars.discourse-cdn.com/v4/letter/m/ac91a4/32.png) [@mattwilliamd34](https://community.cartalk.com/u/mattwilliamd34)\ **Post date:** [July 22, 2017, 4:18pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/18 "2017-07-22T16:18:02Z")
Another question is how come you get play in the bolt when you turn the threads like you can move slightly left to right . Surely that is bad because then it wont be aligned as it would come out and be misaligned. ---
**Author:** ![B.L.E](https://avatars.discourse-cdn.com/v4/letter/b/848f3c/32.png) [@B.L.E](https://community.cartalk.com/u/B.L.E)\ **Post date:** [July 22, 2017, 4:54pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/19 "2017-07-22T16:54:49Z")
To complicate things even more, some high strength precision bolts are purposely threaded so that the female threads have a slightly different pitch than the male threads. This is to compensate for bolt stretch when tightening the bolt so that the thread pitch matches exactly when the bolt is torqued to specs resulting in all the engaged threads sharing the load equally. ---
**Author:** ![mattwilliamd34](https://avatars.discourse-cdn.com/v4/letter/m/ac91a4/32.png) [@mattwilliamd34](https://community.cartalk.com/u/mattwilliamd34)\ **Post date:** [July 22, 2017, 5:50pm UTC](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108/20 "2017-07-22T17:50:36Z")
ah that does make sense but it baffles me how it could have play when turning the bolt up by hand only slight and you can feel it if you did it by hand like tilt left or right , how is tht caused . [Next page](https://community.cartalk.com/t/pitch-size-and-diameter-of-bolt/106108.md?page=2)