standard air filter

My air filter came off yesterday and lost the screw that holds it onto the transmission case. Any one know where where i can get one or what it looks like so i cab have a look in the shed
for one

 

M6, Philip's head about 60mm long for the front bolt and 30mm for the rear.

 

Its the one in the middle where there's a little lip on the transmission case, and there's no thread on there its just circles

 

The captive thread for the bolt is on the mudgaurd.

 

Okey cant say i say it but will check in the light and not at work what size and type is it ?