OTC Tools OTC 5603 Deep Well Connector for Compression Tester. Use with OTC compression testers or other compression testers with a standard quick connect. This unique connector allows easy access to hard-to-reach spark plug hole on Hemi style and recessed plug well style heads. Features and Benefits: Solid steel 8 length shaft. Upper t-wing grip for ease of installation and removal. Popular 14mm thread for both flat and tapered seat plugs. Corrosion resistant nickel plated finish.