This Mikuni Needle Jet is identified by the numbers 568 being stamped on it.   The Mikuni 568 series is used in Mikuni RS34, 36, 38 and 40mm carb sets as well as the TM40-6 and TM36-68. These Mikuni Needle Jets use the N100.604 round type Main Jet which is a different thread and sizing scale to the Hex type main jets. There are other needle jets that, although having a different series number stamped on them, are identical to the 568 and thus interchangeable.

The lower the letter and number indicates the leaner the jet. Example P-4 is leaner than P-6.