B-Cups are industrial-grade car suction mounts with 5/16" studs that mount in the outermost holes of our RigPlate. You will notice 3 different versions of suction cups that we offer. The A-Cups are appropriate for most applications. The B-Cups have more holding power in a straight pull but the main reason we offer the B version is that they have less flex so the overall mount is a bit more solid. The trade-off is that they also are more easily removed so if the mount is going to be subject to a lot of outside forces (wind, water, etc...) then the A or C version is recommended. C-Cups are for the most serious of jobs with a vacuum pump mechanism to keep the suction cup securely affixed to a surface with a visual safety indicator.