This is the linear rail carriage mount for the Kossel Mini 3D printer magnetic ball joint upgrade. This carraige uses four M3 bolts to mount to the HIWIN style linear rails found on Kossel Mini Delta 3D printers and holds the GT2 belts.It is a component the the Kossel Mini Magnetic Ball Joint Upgrade ( https://www.shapeways.com/product/X42BK2G2T/kossel-mini-effector-body-for-magnetic-ball-joint )
NOTE: In order to complete the upgrade you will need three of these, one for each tower of the delta printer.