It's labeled as part LL. It's glued onto the balsa stand off MM which is glued to the glider. The dowel fits into the Transport launch lug EE, not to be confused with launch lug V. This holds the glider secure during ascent.
See page 10 of instructions, "Attaching glider launch lug".
(Probably they should have called it a dowel instead of a launch lug).