JMP Chrome Fork Tube FORKTUBE_JMP_7730791. 1x Chrome JMP Fork Tube. Product Type: Fork Tube. Outer Diameter : 41 mm. Inner Diameter : 37.4 mm. Connection Top : Internal Thread. Bottom Connection : External Thread. Thread : 39 x 1.0, 41 x 1.0. You can send us a message by using the “Questions and answers” section towards the bottom of the page.