This is a complete hot end effector for delta style printers using magnetic attachment. the 10mm balls are bonded into the effector plate and are at 43mm centres. the effector clamp is for the smaller plastic style j-head hotend. the mk2 version of effector plate has a slot for the hotend for wiring to pass through, giving a cleaner look to your printer. It is slightly smaller than the mk1 version. The effector mount requires 2 x 30mm fans and 2 x 40 mm fans.