NGK B7HS (short reach) spark plug.
The grade listings and applications for NGK spark plugs are as follows :
B7ES - long reach / town and city use / for a standard engine
B8ES - long reach / local and distance use / for a standard or midly tuned engine
B9ES - long reach / competition or distance travelling use / for a tuned engine
B10ES - long reach / competition or full race use / for a high tuned engine / sidecar use
Spark plugs with a 'BR' denomination have a built-in resistance and are designed for use with delicate electronic equipment (such as SIP rev counter / speedo units).
Spark plugs with a 'HS' denomination are SHORT reach versions (usually utilised for early pre-S1 Lambretta models manufactured between 1947-'57).
Lambretta models that use a SHORT REACH spark plug are: A + B + C / LC + D / LD + E /F + Lambrettino 48
Lambretta models that use a LONG REACH spark plug are: S1 + S2 + S3 + GP / DL + J (all versions) + Lui Vega Cometa + Serveta