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. 
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.

3/8" drive 18mm
Chrome Vanadium steel, durable.
Socket Suitable for Spark Plugs with 18 mm Hexagon.
Dimensions of socket:
Outside Diameter 23.9mm.
Overall Length 70mm