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If one is trying to remove a stuck square-taper bottom bracket, it is hard to both hold the tool onto the bottom bracket splines and turn it at the same time. Many tools, like the Park BBT-22, have a hole so you can bolt it down using the crank bolt hole in the spindle, so you can just focus on turning it, or so you can just hold the tool in a vice and use the bike frame as a lever.

However, documentation seems fairly sparse about exactly which bolt one needs for this. Obviously it's like a crank bolt, but longer. But what's crank bolt threading? What length works best? This forum thread has the advice "Get an M8x1.0 bolt 40 or 50 mm long. Note the thread pitch is 1.0 mm, not the more common 1.25 mm that is usual on M8 bolts." Can someone confirm that is correct? It seems hard to mess up the threading, but the answer is from thirteen years ago, refers to a BBT-2 rather than BBT-22 (typo?), and it's not clear what length is optimal. Hoping someone has such a bolt in their tool drawer and can just measure, so I can order the best bolt (and I'm sure I won't be the last person to have this question).

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There’s actually a tool made specifically for this purpose. For example, here’s a link to the Pedro’s version:

https://pedros.com/products/tools/pedal-crank-and-bottom-bracket/bb-socket-holder-ii/

They call it a “bottom bracket socket holder” so try that as a search term for others.

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  • Wow. Pedro's makes some inventive tools. This and the Vice Whip. – joseph_morris Nov 26 '19 at 6:40
  • this is what we use at the shop, sans the spring – Nathaniel Hoyt Jun 26 at 20:39
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I also emailed Park Tool, and C. Calvin Jones wrote back and said "[T]he M8 x 1mm x 40mm does the job nicely. Another way it to use a quick-grip. Of course this fills the hole where the torque wrench would go during tightening." So that seems pretty definitive. (A "quick grip" is what I'd call an "F clamp" or "bar clamp").

In a pinch, I recently used a bolt of the right diameter but wrong threading, which worked. I thought it would be destructive removal of the bottom bracket, but because the spindle was hard, high-carbon steel, it was the bolt's threading that got destroyed and the bottom bracket came out intact. YMMV.

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The square hole in a Park BBT-22 as actually for a 3/8 socket driver (9.525mm so a ~8mm bolt will pass through it).

I suspect that the thread may be different for different bottom brackets. Take the crank bolt to your local hardware store or wherever has a good selection of nuts and bolts. Find a nut that fits the bolt, then get a long bolt with that thread.

You don't need a bolt that is exactly the right length to tighten up on the BB tool before it bottoms out in the axle. Either get a stack of washers and add or remove as necessary or a bolt that is a new cm too long and thread a nut onto it that you then tighten up on the BB tool once the bolt is threaded in the axle securely.

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