“DSR” Hubs - for assembly with “AR” plate sprockets to create double-single of substance sprockets. Finish bore hubs have got regular keyway and 2 READY SPROCKET HUB TYPE DSR setscrews.
Ready Sprockets are an assortment of sprockets and hubs drilled and tapped for basic, convenient assembly with standard hex head cap screws. 
For No. 35 through No. 100 Chain, with stock completed bore hubs to support shaft sizes through 2-3/4″ diameter, plus a variety of sq ., hex, spline, and tapered essential bores.