Air filter with a 42mm inlet suitable for pre-65 trials and many Japanese applications as follows:-
BSA / Triumph etc. all 376 Monobloc and 600 Concentric Carbs
Honda MTX200, XL250RC, CB650F
Kawasaki KL250A/C, KH400, Z400/750/900 Z! A/B
Suzuki GS125ES, TS185ER, RG250 Gamma, GT250/380/550
Yamaha DT/RS/RX100, RD250/350/400
The filter is approximately 75mm at it's widest point tapering down to approximately 50mm. The overall length is 80mm from back to front. The end caps of the filter have a nice deep chrome finish.
These filters should always be oiled before use for maximum filtration efficiency. K&N Filter Oil is available from this site