John.
Thanks for the reply, I did a search and found the attached chart. Shows that 5-40 is a 5ba metric. I checked Micro Fasteners site and they don't have that thread listed. I might just give them a call and see what they recommend.
Best, DennisT
OK, I cannot help myself, I suppose. It *is not* 5BA. I recently guessed that they must be 5BA, and acquired some (which is not that easy) and it's pretty close, but 5BA is the right diameter and the wrong pitch, it will start, but only go about 2 turns before beginning to bind up. It's finer pitch than the stock screws, and further off than a 5-40, which is also slightly too fine.
It is also clearly not 5-40, but 5-40 is far and away the closest of any known standard size, and is satisfactory over the depths of engagement required on ST46s and 60s. That's what most people use on ST46s and despite the epic arguments from the past, will not damage anything.
Of course, the original stock screws are also entirely satisfactory and do not need to be replaced. Standard screwdrivers with the right thickness are generally far too wide to fit down into the head fins, and the ones that do fit in the fins are way too thin at the end. Just like "Phillips" and Japanese cross-head, to be safe and not damage the slots, the screwdriver must exactly fill the slot, in both dimensions, and there should be no "slop" or more than infinitesimal rotation of the blade in the slot.
I have an old Proto electrician's screwdriver that I had to grind much blunter, and to remove the angles from the blades (it's now hollow-ground so the faces of the blade are parallel, and thus not prone to pushing out of the slot when you apply pressure). It's the same principle as gunsmith screwdrivers.
The closest commonly available screwdriver to fitting that I have found is a Craftsman 3/16" Cabinet Screwdriver, #41427:
https://www.amazon.com/Craftsman-9-41247-Cabinet-Screwdriver-16/dp/B00065T9RY This one is about the right width and will fit down in the fins, but, as above, you have to grind off about 3/32" from the tip from the way it comes to make it fit the slot properly. It has ridges on the faces of the blade, so leave off the grinding so the peak of the ridge fills the slot. Most people use a standard 1/8" flat screwdriver, which fits down in the fins OK, but easily rotates 15-20 degrees because it is far too thin. You might be able to get it out, but it will distort/damage the slot by riding on the corners of the blade instead of the flat part.
If you damage the screws - any screws- removing and replacing them, that means the tool didn't fit correctly. The hallmark of good workmanship is not leaving evidence of having worked on it, like distorted screw slots, scrapes, etc.
Brett
Topic: ST60 screw set - size? (Read 1617 times)