Gates G25100-0406 4G-6MP MegaCrimp Coupling, 0. 25" Hose ID, 3/8-18 Thread Size. MegaCrimp couplings give you a leak-proof seal. The "C" insert allows usage with different constructions and wall thickness. In addition, the "C" insert ensures an even distribution of crimping forces to form a concentric seal. That simplifies your inventory requirements since one size can accommodate many different hose ODs, on both one and two-wire hoses. An additional bonus: MegaCrimp couplings are a fully qualified EN-performance coupling.