21 mm Pro Plug Socket from Motion Pro.

Features:

• Fits 21 mm and 13/16" spark plugs.
• Ultra-strong tool steel construction.
• Slim skeleton profile.
• Use with a 3/8" square drive or 17 mm wrench.
• Innovative internal plug retention system.
• Protective black oxide coating.
• Easy to read laser etched markings.
• Can be used as an axle-holding tool on bikes with 17 mm or 24 mm internal hex axles. Through hole allows use of a screwdriver or holding rod.
• Lightweight.
• Patent pending.