The K comes with 4-4 pipes as STD but the F series all have 4-1's.
The 4-4 pipes have a different fitting arraingement at the head, these can be fitted to either series but you need the whole assembly.
The K has spigots that bolt to the head then the header pipe slips over this and is held in place by a clamp that pinches the header pipe.
The F series has a flange on the end of the header wich is pushed into the head by split collars held in place by the large round clamp.
Supperficialy they look very simmilar, if you look at the large clamp arround the header, the one with the cooling fins in it, you will see the K one is split on one side with a pinch bolt, the F will have 2 studs holdong it directly to the head.
Most K's that have 4-1 fitted now have the F style monting used as this has become fairly standard on just about all bikes these days.
