NGK spark plug BR7HS (alternative for Solo order number 23 00 500).
Specifications are identical to the NGK B7HS, however this is the "suppressed" version, which prevents disruptive noises on electronics (including radio).
Is fitted as standard by Binder on their EB aircraft with Solo engine.

Can also be used as a replacement for the no longer available Bosch W5AC and Champion L82C.
Spark plug cap size 20.8mm.

Technical information from Solo:
Previously in all engines and variants of the series 2350 and 2625 spark plugs from the manufacturer Bosch type W5AC were installed.
Bosch has stopped the production of these spark plugs. In the future, spark plugs from NGK type B7HS will be installed.

We recommend using a torque wrench at all times when tightening the spark plug (according to the prescribed tightening torque of the engine manufacturer).
We supply various torque wrenches at attractive prices!