Enclosure assembly, screws not fitting into locks
Hey, I'm still new to printing here at the library, we (current public library maker lab team) both started in September.
Context: We ordered an enclosure for the MK4 printer so folks won't burn themselves (again), but assembly has been a little tough.
Problem: There are locks that require insertion into Handles so that they can be held in place to insert the screws. Problem is, NONE of the screws that match the label will fit into ANY of the locks. We struggled with it for a total of 30ish minutes. We've skipped the step for now and assembled majority of the enclosure up to preparing to insert the printer, but I want to wait until we get those Locks and Screws in place.
Any tips on this? I've tried in the enclosure itself, I've held it in my hand and tried to get the screw to catch in the internal thread, I've even tested a couple of other screws. I'm thinking of pushing my screwdriver in to maybe open the hole a little so the screw will actually catch. But any advice would be greatly appreciated (especially by my boss, who is currently on vacation, and would very much like this expensive thing assembled by the time she returns).
-BLR of the Virginia Dillard-Smith Public Library Maker Lab
The lock and screw in question, that refuse to connect. 
The partially assembled enclosure without the internal locks.
I suppose a library is a little short on tools 'though you should have good connections: You need a set of taps and dies, specifically thread-cleaners. Contact a local engineering workshop and see if you can borrow some for half an hour ...
Beware, they might fine you for late return.
Cheerio,
RE: Enclosure assembly, screws not fitting into locks
Assembly of the PSU-lock parts shown in your photos is described from here: https://help.prusa3d.com/guide/3-assembling-the-enclosure_563346#564501
The screws shown in the photos look like the correct size (M3x8), but you show a package label with M3x4. M3x4 are too short.
I would be very careful using a power-tool for the M3 screws on this enclosure. This could destroy the threads very easily.