Bought a forearm for my BT99. I have the big fat one on it now. I bought the slim one. Looking at it, there is no way the iron on the fat one will fit the slim one. The fat one has a screw from the out side front, the slim has no place for it. The slim one is about a half inch shorter where the latch would fit. I guess there are different locking parts for different fore arms. If I was up North I could use it for fire wood. Oh well life is not easy.