The brake master cylinder of OEM MC39646 is aluminum made brake cylinder, which fits for Chevrolet, Dodge and GMC heavy duty vehicles. And the reservoir material is plastic. As for the rubber, its material can be changed as per your brake fuild requirement. The bore diameter is 1-1/8" or 1-7/8". There are two outlet ports. The primary & secondary thread size are both 1/2". The Interchange Part Number as follow: 10-2352, 174-668, 18M1746, 18M361, 783-44021, 83-44021, M900567, M-86021, 12219, 130.66021, 131.66021, MC116881, NM2219, 2539646, MC39646, F116881
