A light-hearted jest prompts the serious question: how does your team handle multiple thread pitches of the same diameter screws and nuts?
On one mechanism of our 2020 robot in particular, #10-24 and #10-32 hardware ended up being used interchangeably. This proved a real issue, especially when we disassembled things to make changes. Many a brave little locknut lost its life to the evil cross-threading monster. Yes, it’s possible to tell them apart, but in the heat of build season and with screws strewn about, the tendency is to just try the fit.
Is the easiest solution to keep only one in stock? In that case do we opt for finer or coarser threads? What about specifying carefully in drawings? Stocking them in distinguishable finishes?
IMO this is the easiest solution. There’s a lot of benefits to minimizing the amount of unique fasteners on the robot.
I find the choice of fastener to standardize on dependent on the COTS ecosystem you tend to use. If you use a lot of VexPro products, it might be worth standardizing on 8. Most other suppliers seem to stick with 10. There’s corresponding pop rivet sizes as well (5/32" for 8 and 3/16" for 10).
If you’re doing 8, definitely stick with course thread (#8-32 is just much more common). With 10, since the CIM mounting pattern and all the products derived from it are #10-32, we stick with that.
Like others have suggested: only keep one in stock.
Our standard is 10-32 & 3/16 rivets as our primary fastener. 8-32 and some 1/4-20 for Vexpro items and tapped holes (churro & thunderhex). When we formed and were primarily on the COTS/AM standard we used 1/4-20 everywhere. Now that we are into more custom assemblies and the age of Versaframe the #10 & #8 is more common in our shop to reduce how much we drill out.
We do have a box with some assortment of 10-24s from a few random mechanisms over the years that involved #10 shoulder bolts that only came off McMaster in 10-24. They get their own bin with extra labels on them in large letters “THESE ARE NOT 10-32s!!” Education is key - how to recognize and where we keep things.
Works okay until you are struggling to assemble something and realize you got a 10-24 nut… and another after that. Might ban them.
We have some #10-24, mostly for all thread. So not much need for bolts, but we have a box of nuts and they get spray painted yellow. That makes it harder to confuse them.
Don’t forget: ALWAYS have and use a thread gauge when returning parts to the parts bins.
I would go for “only one in stock” wherever possible. 10-32, for that particular size (10-32s tend to resist tension loads slightly better as I recall). If you MUST go with 10-24 for any reason: They stay in the original packaging, and you mark them. I’m not sure I’d go so far as to do a distinguishable finish–that could potentially cause issues later in life–but if you do make sure that ANY non-standard fastener gets that finish. (e.g.: “standard” gets black oxide, “non-standard” gets something shiny and not black oxide)
And whatever else you do: don’t let the metric hardware get anywhere near the standard hardware. Some sizes are “close enough” that you’ll cross-thread or mysteriously jam–the worst is the nearly-identical M8-5/16-18 pairing, with M6-1/4-20 right behind it.
One approach I looked into a few years back (and got to the point of building a very rough prototype of was to have labels that double as ways of identifying bolts.
We standardize, after learning the lesson the hard way. Our rookie year we had a mix of 10-24 and 10-32. We’ve since moved shop locations multiple times and gone through our stock bolt by bolt… and we still have the occasional 10-24 nut or bolt show up!
We try to order blue color for anything metric. M5 and 10-32 are really close. For the rest of it, you can tell by appearance after a while, and we still keep gauges around for the oddball stuff.
This is the one place I’ve struggled, 1/4" shoulder bolts with #10-32 thread seem to be much, much less common and much more expensive than their #10-24 counterparts.
Dr. Joe Johnson also expressed some thought on 10-24 on this forum on some occasions, IIRC. That was in the distant past.
10-24 could replace every thread size on an FRC robot if every component was scratch-built. However, the COTS ecosystem has evolved to include many other threads; the irony is that 10-24 now should be BANNED, as many others have suggested.
Just a sidetrack to pine about the metric system:
They figured out the sweet spot. All the standard thread pitches are inbetween UNF and UNC, which makes for a good middle ground, which eliminates the thread pitch problem because noone has much incentive to be fine/coarse.
But yes, standardize english. In experience this means: #4-40 #6-32 #8-32 #10-32
(No #12)
1/4"-20
5/16"-18
#10-24 and other oddballs get their own bags labeling exactly what the hardware is.
(Unless you’re in automotive, in which case 1/4"-28 and 5/16"-24.)
Despite every effort to standardize, there are always situations where we have to accept a few exceptions. For example, many pneumatic cylinders use 1/4 -28 threads on their piston rods, so the associated jam nuts that come with those cylinders are one exception to the standard 1/4-20 hardware. I can’t recall what caused us to include some 10-24 hardware in our bins along with the standard 10-32. And there are several vendors that sell parts that require metric hardware as well.
While we try to separate them as best we can, mistakes are bound to happen and hardware ends up getting mixed together.
So, the main solution we have is to train the students that the bolts or nuts should be able to thread easily by hand up to the point where the locking feature engages. If it does not thread easily by hand then don’t force it. It is probably the wrong thread (or the threads are buggered). Get a new fastener out of the bin that can be installed easily by hand and set aside the one that doesn’t work. That training seems to have worked well for us and also helps the students understand fasteners a bit better.
