A S-type nock are nocks made to fit a .246 ID,like in alot of carbons and aluminum uni-bushing 20XX and larger.Easton calls their S-nock Super nocks,I like their 3D Super nocks as they have the largest and deepest throat of the S-type nocks I've found.The Easton 3D Super nocks are alittle different then Easton Super nocks,they have a slightly larger throat.Signature nocks fit the same .246 ID,they are made by Bohning.Bohning makes a good quality nock,I use them also and never had any problems with them.Easton 3D Super nocks are close to a Bohning Classic but don't have as large a throat.You could if you like Bohning Classic nocks you could use a nock adapter in carbon and use 5/16 glue-on nocks.But I like to be able to replace those nocks and be able to rotate them.Take a look at the 3D Super nocks,they are my favorite S-type nock.