Beam caliper is your bud.

They're 3/16" (4.7625mm) hex. I always use a 5mm hex socket because imperial sizes are hard to come by around here.

Those sets with various hex socket sizes usually include an adapter bit for 1/4" hex screwdrivers. (edit: pic)

I've often just used long nose pliers, I didn't realise there are special tools for them?

I only use my fingers to screw and tighten mobo standoffs in place. Only use pliers to remove those that are very tight or stripped. Never had a need to use anything else.

dacow wrote:

I've often just used long nose pliers, I didn't realise there are special tools for them?

Lian-Li and others used to give them away with case purchases - it's basically just a hex driver. I'm with JayCeeBee64 though: on cases that actually have screw-in standoffs (a lot of mine use pins or clips or are permanently anchored etc) I just put them in by hand. I've seen those things snap off pretty easily, so it's nothing I'd want to take a ratchet or power tool to. 😊

if you have a screwdriver with interchangeable bits, can't remember if the hex fitting of the handle is the right size.

There are also sets that have a hex to square adapter as a socket driver - and using a screwdriver handle instead of a spanner is better to avoid overtightening.

Smaller scale tool - nut driver / nut spinner

Matth79 wrote:

if you have a screwdriver with interchangeable bits, can't remember if the hex fitting of the handle is the right size.

Usually not - it's usually the right size for the hex-head screws though. 😀