This nub is only made for TDC mod for tippmann airsoft m4
you have to take the original nub out.
drill the hole throug rail an half the way down in the i use 9,5 mm drill
the i cut the thread with a m10 cutter.
put your nub down and a m10 hex on the top. then your are done.
to gain more shot leght remove all inside your hopup bucking. search on youtube
"flatnub"