This air filter was manufactured for motorcycles during the Second World War by Vokes Limited of Guildford. The air filter is 220 mm long by 176 mm wide by 48 mm deep. It rests on the petrol tank with three felt washers, one either side and one at the front. It is secured to the petrol tank on either side by two adjustable clamps and the plate securing the clamp to the filter body is set at a slight angle to take into account the roundness of the tank. The clamp itself secures to the petrol tank via the rearmost kneepad screw, being naturally under the kneepad itself.

The air enters the filter via a ventilator plate on either side and also through removable plate which forms the airfilter base. This base plate is held in place by four clamps. Once inside, the air is actually filtered by five felt tubes. At the rear of the filter body are ten outlet tubes. The felt tubes are secured to these ten tubes at either end by clips, the felt tube itself being stretched round one of two bars, at the forward end of the filter body. After going through the felt tubes, the air ten passes via the ten outlet tubes into a sealed air chamber and from there it is ducted via a single outlet pipe 28 mm in diameter on the offside rear, to the carburettor air intake via an armoured, flexible air hose.