1/4 x 2 Slotted Spring Pin. Used as top stop on TM12 and PMC24 Houses. 

• SSP Pole (For TM12 House): This pin is inserted into the hole that is located 5-1/2" down from the top end of the pole.
• CP24 Pole (For PMC24 House): This pin is inserted into the hole that is located 4-3/8" down from the top end of the pole.