Seems like most of what we read regarding sizing classes pertains to anthracite. Bit. and Anthricite can both be called nut, egg, etc, but sizes are different. Maybe this info I found on web (http://www.sizes.com/materls/coal_bituminous.htm) will help some with Bit. sizes/classes:
Run of mine - goes through 8-inch holes
Lump - goes through 5-inch holes (hand firing and domestic purposes)
Egg - goes through 5-inch holes, retained by 2-inch round holes (hand firing, gas producers, domestic firing)
Nut - through 2-inch holes, retained by 1¼-inch holes (small industrial stokers, gas producers, hand firing)
Stoker - through 1¼-inch holes, retained by ¾-inch holes (small industrial stokers, domestic firing)
Slack - ¾ inch and under (pulverizers and industrial stokers)
Also a list for anthracite at http://www.sizes.com/materls/anthracite.htm.