on the '67, it's part of the frame...one way to tell a P11 from a P11A or Ranger.
It's about a 1/2" tube brazed to the frame near the top shock mounts. It would have two tabs brazed to it to hold the front of the rear mudguard on the back, and two pins on the front side to hold the seat in place (similar to the pins for the tire pump on other models). The front of the seat (fiberglass pan) has a tongue that slips under the fuel tank. 4 bolts hold the fender to the bike (2 at the frame loop through the tabs, two at the rear fender loop through the tabs)
On the P11A, the seat was about 5" longer, and the rear fender loop has a flat bracket welded to it, about 1" wide and 1/8" thick. This bracket has four 1/4" holes in it - two on the flat parts to take the studs on the rear of the seat, and two on the radiused center to mount the front of the mudguard. Again, the P11A pan is fiberglass and serves as mudguard, too, for about 10". 4 bolts hold the fender to the bike - 2 through the bracket on the front of the loop and 2 through the tabs at the rear of the loop)
On the Ranger, the seat is different again. The rear fender loop is similar to the P11A, but only needs the two holes on the radius part to mount the fender. The fender on the Ranger extends under the seat and terminates at a tab brazed to the rear cross tube on top of the oil tank (five 1/4" bolts in total mount the Ranger fender to the bike). The rear of a Ranger seat has a bracket bolted to it that is secured by the shock top bolts. (The seat pan is actually the same steel pan as late G15CS/N15CS bikes, with different mounting method for the different frame)
