High professional bass drum trigger system for the installation into an acoustic drum (conversion into electronic drum)
The terms M4 and M5 refer to the diameter of the threads of the screws that attach the lugs to the drum shell. M means metric.
M5 = diameter of 5 mm
To determine if you need the M4 or M5 version, you can measure the diameter of one of the attachment screws of the tuning lugs with a sliding caliper.
... Compatible with all drum modules and manufacturers !!!