Yes, they are nitrated or something but once you cut thru that they machine pretty nice---I really like the milodon nodular caps but them and the programs are expensive----we are doing conversions on sbc 2 bolt blocks because its almost impossible to find any decent 4 bolt blocks these days--the 4 bolt blocks are pretty old, rusted away on outside, broken bolts, cracked mounting ears in back, etc--two bolt one pc seal blocks are reasonably available and we are putting a lot of splayed bolt caps on--also have billet 2 pc seal adapters from K tech but they are expensive---can get the dogbones and spider trays for the roller cam blocks----also do a lot of dart shp blocks