Tohnichi's interchangeable head wrenches have specific diameter round ends that fit into corresponding head base openings. Head and wrench model names include the diameter sizes so that heads can be matched to wrenches that accept those heads. With the large selection of head styles available, wrenches such as CL (for tightening) and CEM3 (for measuring) can use the same head that has the same root diameter--making interchangeable head wrenches an economical and flexible tool choice. Features: Model Applicable Models FH15D X 45 CL50N ~ 140N / CSP / PCL, YCL90N, 140N CDB100N-S, CF100N, CEM90N2, CTA100 / CTA-P / CTB