NGK BR10ES long reach spark plug (resistance type for use with SIP speedo's)

NGK BR10ES 'long reach' spark plug ('RESISTANCE' TYPE for use with SIP speedo's) 

The grade listings and applications for NGK spark plugs are as follows : 
B7*S -  town and city use / for a standard engine 
B8*S -  local and distance use / for a standard or midly tuned engine 
B9*S -  competition or distance travelling use / for a tuned engine 
B10*S - 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