If you want to mount a Bobber or a solo seat to your frame, then this kit is exactly what you need. The seat springs go over the Ø12mm pen. The kit contains two pins that you can either weld to the frame or bolt with the supplied stainless steel M8 Allen bolts (round head).

They fit perfectly on a frame tube of 1" (25,4 mm) but also fit a larger tube. Moreover, the rubber rings protect your paint from eventual damage caused by the springs and ensure these do no squeak. 

Spring height: 2" (50,8 mm)

Pen material: good weldable steel