We use the ASTM specifications for bolts and nuts (F593 and F594, respectively). I don't use toolbox, and have configured our fasteners to be two parts, fastner with washer and nut with washer. I assign the following material to the fastener with washer and exclude the nut with washer from the BOM. That way all my hardware information is in one place, with properties linked to the actual dimensions from the part. I came to this after many iterations and that is the best I could come up with. Here's my spec for something similar to 18-8:
ASTM F593 GR. 1 OR 2 COND. CW, ASTM F594 GR. 1 OR 2 COND. CW, ASTM A240/A276 304/316
F593-Fastener, F594-Nut, A240/A276 Washer.
Here's a pdf with information summarized from the ASTM:
Additionally, Portland Bolt has a lot of good information on fasteners:
If you want to really nail down the specification, the ASTM will enable you to get exactly what you want. However, it is going to cost more than just specifying 18-8. Also, if you use hardware under 1/4" or larger than 1 1/2", you'll have to find a different spec.
Good luck and let us know what you come up with.
for now I will use ANSI B18. which is the dimensional spec, specifying 316 is close enough for material.