The following needles will fit Laser II and any other brand tagging gun which uses Dennison-style needles (with the cutting blade built into the needle).

#300 is the regular needle and fits standard tagging guns.
#600 (same as #700) is the heavy-duty needle and fits standard tagging guns. It is thicker than the #300 and makes a larger hole, but does not bend easily.
#400 is the fine needle and fits fine guns only.

The following needles are used in Monarch-style guns (where the blade is separate):

#T94 is the regular needle for standard guns.
#T97 is the heavy duty needle for standard guns.
#T44 is the fine needle and fits fine guns only.
#T50 is the long needle and fits long guns only.

NOTE: 99% of tagging gun problems will be solved by inserting a fresh needle!