JMP Chrome Fork Tube FORKTUBE_JMP_7731542. 1x Chrome JMP Fork Tube. Product Type: Fork Tube. Outer Diameter : 41 mm. Inner Diameter : 36 mm. Connection Top : Internal Thread. Bottom Connection : No thread. Thread : 37.5 x 1.0. You can send us a message by using the “Questions and answers” section towards the bottom of the page.