I grew really tired of the original UM2 Bondtech motor mount having it's nuts slip out over time. So I designed my own. Normally I would use metric as the rest of this printer is metric. But this uses Imperial screws and nuts as they provide a bigger surface area to hold the mount together without trying to get a nut and washer iide the mount base. This assumes you have the QR Ultimaker 2 Kit: Non-Printed Part List Two 6-32 screws of 3/4 inch long Two 6-32 nuts (not lock nuts)