We just got a shipment of a variety of AR-15 bolts from Toolcraft and the bolts were all mixed up in the box and unlabeled. So I got a crash course in sorting bolts by the bolt face size. I figure this might happen to one of ya'll so I'm sharing what I learned. You'll need some calipers or super precise ruler to measure.
I also did a bunch of googling and identified the (in)compatibilities between bolts for different rounds. This can be quite important to know if you're shooting grendel, if you mix up a Type II Grendel bolt with a Type I Grendel barrel, the bolt will close but the headspace will be 11 thou too loose and you're gonna have a bad time.
(dimensions are approximate, but precise enough to differentiate)
Cartridge Bolt Face width Bolt Face depth Also used by 5.56x45 0.380" 0.125" .223 Rem, .204 Ruger, 6x45, .300 AAC Blackout, .277 Wolverine 6.8 SPC 0.425" 0.125" .224 Valkyrie 6.5 Grendel Type II (SAAMI) 0.450" 0.136" 50 Beowulf / 12.7x50 .458 SOCOM 0.475" 0.125" .375 SOCOM, .450 Bushmaster 7.62x39 0.450" 0.125" 6.5 Grendel Type I (rare)
the 308 bolt is easy to pick out because it's massive.
sexy bolt pic. The one on the left is nickel-boron. we have this option for most sizes at the time of writing this. Click the pic for the product