Basic rule, pro saw use rim drive clutch drum(splined hub) and non pro saws use sprocket drum. Drum is a wear item as sprocket/ rim should be changed about every two or three chains. clutch drives the drum so inside wear from that, yearly replacement for pro depending on use. Drum rides on a bearing another wear and service issue. Also the brake band runs on the outside of the drum. This all boils down to if your saw has sprocket drum run it until replacement is needed then change to a rim drive, cost is about the same but the rim system allows you to only change the rim which wears 4 or 5 times faster than the rest of the drum. The sprocket drum type is one piece. Rims are $ 8/$ 10, sprocket drums $ 25, rim drums w/rim $ 25 or so. Also the rims allow you to size and pitch by just changing rims. I' also recommend starting with at least 3 chains and rotate them. 5 is even better if your having them sharpend by someone else. This allows you to have some in the shop and still have spares when cutting. You don't want to run a chain til it's dull, when you have to push it change it. When chains are rotated the rim and chains are meshed and wear longer. This may seem an expensive way to do it but if you use one chain a year normally this way will last five and is more convienet. You may want to try 3 different styles of chains first even if you find a favorite you can hang up the other two and by more of your favorites. Hope this helps out. Ken