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The Swiftech MCP35X Housing (Single DDC) has M4 internal threading at each corner, while the new Swiftech MCP35X2 Housing (DUAL DDC's) has USA 8-32 internal threads at (8) places. M4 metric & USA 8-32 screws ARE NOT interchangable. Swiftech supplies/uses a Hi/Lo self threading screw instead of machine thread screws - the self cutting screw may push POM/Delrin cuttings into the drilling, preventing the screw from fully drawing together the ddc pump body and the swif custom top(s) - the leak reports may be due to o-ring not fully clamping to make water seal

EK exclusively uses M4 internal threading at all ddc pump top hold down points

I prefer to assemble my personal ddc's using machine thread studs and round cylinder "nuts" to more accurately control ddc pump body clamping force.

Be careful if you are installing the Swiftech provided Hi/Lo self threading screws for FIRST time - and be certain the drilling is clear of POM/Delrin shavings before final assembly with main o-ring.