Touch-Mi clone

This is clone from hotends fr's design.
Use M3 screw, neodym magnet ball 3mm and opto sensor.
The screw head must be filing to fit into the opto gate.
Use screw without full thread.
Opto sensor:
http://s.click.aliexpress.com/e/_dTOEWeI
Magnet ball 3mm:
https://www.aliexpress.com/item/4000645514490.html
M3 screw like this:
http://www.magnumkft.hu/termekkepek/769/800x600/Toolcraft_belso_kulcsnyilasu_csavar_M3_x_16_mm__ro--839691_BB_00_FB.EPS_1000.jpg