This in addition to my earlier 2017 walk-through of the same 861; The Omega 861 movement has no less than 18x different types of screws, some easy to recognize, some less so. Working on the same movement again, I've done an attempt to catalogue the different types of screws. It may not be perfect, but I do hope it's a help. The screw part numbers are as per the Omega 861 service manual (given already in the walk-through) 2033, 6x 2224, 1x 2237, 1x 2345, 1x  23