Talk:Crankset

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[edit] Pedal Thread Pitch

"with 20 TPI (a thread pitch unique to bike pedals)." - MAlvis (22:46, 15 November 2006)

While Sheldon Brown confirms the 20 TPI, my Sears/Craftsman 50 Piece Tap and Die Set (hardly anything fancy) contains dies of size 1/2 x 20, 7/16 x 20, and everyone's favorite 1/4 x 20. Also, my Park Tool pedal taps are labeled only 9/16 x 20 (LH and RH), and the pitch matches exactly the right hand 1/2 x 20 tap that comes in the Sears set. I'm skeptical of the claim that 20 TPI is "a thread pitch unique to bike pedals." Does anyone have a source or additional information? -AndrewDressel 21:06, 16 November 2006 (UTC)

Okay, so while 20 TPI is the correct pitch, there doesn't appear to be any evidence that it is unique to bicycle pedals. I'll remove that statement. -AndrewDressel 14:41, 22 November 2006 (UTC)

My error, unintended, was perhaps one of wording clarity, not technical accuracy. It is the "size & thread pitch" combination which is unique to bike pedals, see http://www.sizes.com/tools/thread_american.htm , as one of many examples, including your one Sears marketed tap & die set.

The SAE standard fine thread pitch for bolt size 9/16" is 18 TPI, not 20 TPI. No major bolt/nut, tap/die, or thread repair device manufacturer (including any custom product manufacturer I could find) in the U.S. or abroad, offers any products in a 9/16" x 20 TPI combination, even in only a RH tread. After a rather extensive Google search (broadband connection), Park (previously unknown to me) was the only manufacturer I could find which offered any 9/16" x 20 TPI taps, RH & LH threads (which I ordered from the lowest cost net retailer I could find); they do not offer dies in this size.

TPI is an individual characteristic; the reason TPI gauges are routinely supplied in better quality tap and die sets. As with all fastening systems, it is combinations of characteristics which come to be recognized as standards, not individual characteristics. My comment about the "9/16 in. x 20 TPI" combination being quite unique to bicycle pedals is factually correct, an apparent historical but accepted event in the history of bicycle part manufacturers, assemblers and retailers. "9/16 in. x 20 TPI" is neither a United States (SAE: Society of Automotive Engineers, sae.org usually the dominant authority) or a metric standard. Given current practice to manufacture bicycle cranks from aluminum, the 20 TPI standard, as opposed to the national course "9/16 in. x 12 TPI" standard, which provides a much deeper thread, renders bicycle pedal bolts more prone to stripping out the finer/shallower 20 TPI treads within bicycle cranks. It is also the reason many local bicycle shops either carry specialized repair kits for bicycle cranks (generally rated as of poor reliability by many in the bicycle business) and/or sell crank replacements.

The above issues are part of the reason I ended up doing a search on the "9/16 in. x 20 TPI" engineering odyssey. Having extensive mechanical engineering experience and some small scale manufacturing capability, I elected to purchase the Park taps and will manufacture my own steel inserts from center-drilled grade 8 bolts and in-turn drill, tap and epoxy these custome inserts into cranks needing repair. This should end up more reliable than most currently available cranks, in terms of pedal thread toughness.

As such, and for the benefit of others, I would suggest that you correct, rather than delete the comment about "9/16 in. x 20 TPI" being unique to bicycle pedals. Thank you. MA | T@lk 14:56, 26 November 2006 (UTC)

Okay, I've put something back in. -AndrewDressel 18:15, 28 November 2006 (UTC)