JMP Chrome Fork Tube FORKTUBE_JMP_7730792. 1x Chrome JMP Fork Tube. Product Type: Fork Tube. Outer Diameter : 41 mm. Inner Diameter : 37.4 mm. Connection Top : External Thread. Bottom Connection : No thread. Thread : 41 x 1.0. You can send us a message by using the “Questions and answers” section towards the bottom of the page.