This is a mount for a FLSUN QQ-S / QQ-S PRO. allows mounting optical sensors in place of mechanical end-stops. allows for about 30mm additional Z axis. using optical sensors increases accuracy and decreases mechanical failures. will hold truer bed level distances. includes new belt cover with integrated flag to activate switch. end-stops used: https://www.ebay.com/itm/6X-Optical-Endstop-Photoelectric-Light-Control-Optical-Limit-Switch-for-Printer/174334177961?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 Enjoy