Difference between 9/16”x 20 Cycle Pitch and 9/16”x 20 UNS.

[Michael GilliganParticipant @michaelgilligan61133]

Hopper’s practical approach is of course the appropriate one … if this is a repair job.

If the objective is to produce a functional bicycle, then the practical man uses whatever tools and technique are available … to produce something that works [possibly better than the original].

If, however, this is a restoration job on a ‘significant’ bicycle, then it may be appropriate to identify exactly what the original maker used in the first place.

[ the male threads on the pedals could presumably be measured for starters ]

Perhaps the most academically interesting possibility [as yet unmentioned] is that someone has reason to want a Failure-Mode Analysis … in which case the whole can-of-worms is open!

MichaelG.

[HopperParticipant @hopper]

 

BTW, Bill, 9/16 x 20 BSC taps are on eBay UK for less than 10 Quid a pair, giving both the left and right hand taps in one purchase. Significantly less steep than Tracy’s price for one tap. And probably good enough quality for odd use in the home workshop if you are not going into mass production or specialising in Brough Superiors etc.

Search eBay for “9/16 cycle pedal taps” and plenty of options pop up.

[Michael GilliganParticipant @michaelgilligan61133]

Now that ^^^ is expedient

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

As a general rule, it’s bad practice to mix different thread forms as a convenience.  Maybe acceptable as a bodge, but not when safety matters.   Many accidents caused by mixing threads.

One obvious problem is the class of fit might be compromised.   Either:

• Graunching an over tight connection together damages the threads, or
• The connection is weak and prone to vibrate loose because the threads don’t engage properly.

Bodging when a fastening doesn’t need to be strong won’t do much harm.  But avoid bodging if a fastening coming apart will cost money, cause serious inconvenience, or hurt someone.

Back to Bill’s problem, where it seems a thread is already damaged beyond simply reforming it.   How about welding enough metal into the hole so it can be bored out the the correct size, and then rethreaded?   Easier said than done – I don’t have the gear or the skills.

Dave

[Author]

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