The 19 mm x 15 mm black plastic end cap for Jazzy, Jet, & Quantum power chairs is certainly a common part, but one that is easily overlooked. This little plug found stuck onto ends on most of the joystick arms used on PG Drives, Q-Logic, & VSI joystick controllers.
Pride Mobility uses this ubiquitous little part on almost all of their subsidiary brands' power chairs to keep the rain, dirt, and dust from the bracket tubes.
⚠ WARNING California Residents:
Proposition 65 Warning