Help identifying small bolt size please?

[Fatal Swan]

I've just realised the Principia road bike I bought recently is missing one of the two screws on the dropout. A new dropout is the best part of £30 and I assume the bolt sizes are pretty standard, I just need to get an idea of what size it's likely to be so I can order. It's a countersunk bolt with a Torx head (though I could replace both with allen headed bolts), 8mm long. I'm guessing M2, M2.5 or M3 - can anyone help confirm based on the photos?

The frustrating things is that I've had about 3 of those little credit card-size bolt size identifiers that Pro-Bolt send out, just can't find them after moving house!

Cheers!

 

[FluffyChicken]

Re:

Stick it end on, it's the with including thread, you should easily be able to see it then.

 

[Fatal Swan]

Cheers! As far as I can tell it looks like M2.5 then.

 

[FluffyChicken]

Re:

Cheap digital vernier callipers make the job easy. Not a lot from eBay/aldi.

 

[integerspin]

Cheers! As far as I can tell it looks like M2.5 then.

Looks like M3x.5 to me?

 

[Fatal Swan]

For those on the edge of their seats awaiting news of the bolt size - it turned out to be M3 x 8mm after all, job done.

If anyone needs a pack of ten M2.5 x 8mm countersunk allen head screws for the price of postage, let me know... :facepalm:

Thanks for the help, lesson learned on the digital caliper front!