This is a corner clamp designed to fit the 3018 CNC mill / engraver. Secures with 3x M4 x 14mm screws. Includes 3D printable M4 T-Nut which accepts a regular M4 nut. The nut is designed to be a snug fit (the hexagonal recess is 7mm AF) - simply tighten a screw to pull the nut into the printed part. The parts are designed to print easily without supports.