Using an optical switch instead of mechanical type, this advantage is no springs reaction force formed when retracting the probe. You can write about a g-code instruct effector downward to rise the probe, and then attracted on the top side by a magnet. BOM 1). Mount - printed layer 0.3, infill 30% be enough. 2). optical switch - I think easy to find as the figure shown type. 3). M4 wrench - Across flat is 2.5mm, 60mm long, must metal type that be to attract by the magnet. 4). 10x5x2 Magnet - Normal not need strong 5). M3 x 35mm x1pcs 6). M3 x 18mm x 2pcs 7). M3 x 8mm x 2 pcs 8). M3 nuts x 3