A30-CIR is a screw threaded fuel cap the will fit almost flush to a skin, with the riveted flange on an adjacent tank or the back of a 'wet' skin.
This was designed to be fitted after painting, reducing the likelyhood of dirt/dust in the cap and the cost of masking/finishing operations.
It is available with a locking or non locking cap.
A30 L-CIR (05-06838) Locking
A30 S-CIR (05-06837) Non-Locking