The OS FS-30 manual specifies 3mm screws. Most likely that's equal to a 4-40 standard screw. At home improvement stores like Home Depot you can get a drill and tap that are carded together so you know they match. They might sell the 3mm metric sets but I've never looked. Hobby shops or big tool stores also might stock the metric stuff. Hobby shops sell carded sets packaged by Great Planes and Dubro in the standard sizes.

The Magnum manual, which is also available online, calls for #4 screws. I didn't take the time to look at the Saito manual online.

If you tap the glass filled mount you do not need the lock nuts. They will not hurt anything if you use them but they are not required.