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Strange end ("Double D"? GM?) on a strut rod

Anyone with experience using “Double D” endings on strut rods? (Aka GM Shock Absorber tool?) I tracked down a tool online (link below) that seems to resemble the ends of my strut rods, but there aren’t any specs given anywhere. Do these come in multiple sizes?? I believe I need one that is 7 or 8 mm wide. I saw one online labeled as 7.5 mm wide??
Just trying to get new struts on my VW beetle and very confused about this.

LONG VERSION:
1998 VW beetle, TDI Manual, 240k
Went to change out some very worn struts, but the nut at the top of the strut rod (accessed from beneath the cowl) that holds the whole assembly to the car’s frame is seized. (even after an overnight bath in lubricant) My replacement has a 21 mm bolt screwing onto the strut rod, which ends with a 7 mm allen key hole to hold the strut rod in place while that bolt is tightened. But the one on the car is a 21 mm bolt, with the strut rod ending in just a 7-8 mm wide rectangle that I can’t seem to get a purchase on with any wrench. The internet seems to think this is only used on GM cars, and all VW beetle strut replacement videos show the allen key version. Did some mechanic put GM struts on my VW beetle before I inherited it??

yup . . . you got it

Where? Couldn’t find anything online that actually listed specs. And I’m pretty sure I single-handedly taught the guy on the phone at AutoZone how to change out struts before he finally understood me and said they didn’t stock a part like that.

I meant that mechanics often buy these tools in sets, which would come with the most popular sizes

But my previous comment still stands . . . those flats, if you want to call them that, come in several different sizes

And where could I get a set?

Is there room to get a pipe wrench on it? If all else fails, cut it off with an angle grinder.

This “tool dilemma” is one of the reasons why I recommend buying fully assembled strut assemblies, complete with strut, coil spring and mount . . . you don’t need special tools to replace the whole assembly

Sure, it costs more, but there’s less labor involved, and you know all the parts are new and good to go

In too many instances if you just replace the strut, the coil spring might brake later on, or maybe the mounts will break and/or wear out

If you do the whole thing, at least you can sleep well, knowing it’ll be good for several more years

If the strut assembly is out… and why wouldn’t it be? Cut it off with a friction wheel. You don’t need it anymore, you have a replacement. Just don’t do it until the spring compressors are installed and the spring is loose.

I use an impact wrench set on high and blast the nut off. That tenon is not made to remove the strut, it is there to hold the rod while the nut is torqued at assembly. That little bugger will break right off when you try to use it to remove the nut and then you’ll have wasted money on the tool and still use a cut-off wheel or impact to remove it.

And it isn’t just GM that uses the double-D tenon.

You only going to reuse the spring? Get a complete strut assy

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