they are longer than the NA and shorter than the TT. If you install one in a TT head when the head is off you will find they fit all the way in the chamber ;-) No one makes the full length TT plug in a colder heat range than 6. Since the plug goes all the way in it is a non issue and it is MUCH better to run a slightly shorter plug that is the correct heat range for the application than a longer plug that is too hot.