A mechanical device to lock the Wag-Aero Tow Bar handle when installed on the wheel in order to prevent the tow bar from becoming unlatched.   Material is ABS plastic, brass nut insert and stainless steel bolt.  This is for the 2018 model Wag-Aero Tow Bar that has a .750 inch diameter collaspible long bar.  It will NOT work for the pre 2018 Wag-Aero Tow Bar.   It must be the tow bar shown in the photo that has a left hand orientation.  Fits standard RV-A 6, 7, 8, 9 nose wheel.   Color is white.  
 
The tow bar and posilock can be installed with one hand.  Push the lock in position and flip the wing bolt with your finger to lock.  
 
Wag-Aero RV-A Series Aircraft
https://www.wagaero.com/rv-a-series-aircraft-deluxe-tow-bar.html