Air filter with an inlet of 52mm suitable for pre-65 trials and many Japanese applications as follows:-
Honda CB400N/T, CB650Z, CB750K
Kawasaki Z250, Z400B/G/L, ZR400, Z440A/C/D/H, Z550G/H, GPZ550, ZR550, Z650
Suzuki GS400/S, GSX400E/F/L, GT500, GS550E/M, GT750
Yamaha SR/ XT500, XJ650/900, XS750/850/1100 through 79
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