A conical air filter with an inlet size of 48mm. Suitable for pre-65 trials and many Japanese applications, as follows:-
BSA / Triumph etc. all 389 Monobloc and 900 Concentric Carbs
Honda CB250N/RS CB400N CBX550
Kawasaki Z250A/B GPZ305/400
Suzuki GS250T/E GSX250 GSX400/E
Yamaha DT250/MX 76-78 XS250/SE 78-81 XJ400 XS400/SE 78-82 XT500 76-80
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