Koken Spark Plug Socket 3/8" Sq Drive 16mm (5/8")A/F with Spring  Clip Retention.

Socket Suitable for Spark Plugs  with an 16 mm (5/8") Hexagon 12 mm Thread

Dimensions of socket:
Outside Diameter 20.5mm
Overall Length 70mm

Conventional       magnetic spark plug sockets can adversely affect hi-tech electronic control       devices used on modern engines, but spring clip type is definitely safe    with    that point.

Magnets easily break when dropped or  struck hard, but not spring clip type. The broken pieces possibly stick to the  engine, or get into inside the cylinder head. However the spring clip type avoids  this problem.

The clips are held in place by an internal  brass guide which ensures perfect alignment of the spark plug into the threaded  plug hole of the cylinder head, thus preventing thread damage.

The brass guide eliminates stress loading  and possible damage to the ceramic insulator of the spark plug.