EBC main jets are precise, clearly marked and reliably gauged using pin gauges, and accurate to one tenth of a thousandth of an inch. All jets are flow calibrated and extremely accurate in terms of fuel flow rate as stamped. Mikuni 4/042 hex main jets measure 11.5mm long (6.5mm hex body length/5mm thread length). High precision brass main jets for Mikuni carburetors using 4/042 hex style main jets. Kit contains 2 pieces each jet sizes 240 thru 500 for a total of 54 jets.