[PeterA]

I would suggest that this is the modification plate for the 'Tail Unit'.

6S....Indicates Supermarine as main contractor, so an early IX, if a IX or more probably an VIII

FL.....Indicates usually subcontractor at Filton.

AV....I believe indicates subcontractor to Filton

Mod 193...Indicates a means to draining the fuselage has been incorporated. Introduced on Mks I & II.

Mod 225...Indicates strengthening of the fuselage frame 20 (tail annulus) to cover a) somersault landing b) heavy tailwheel landings. Introduced on Mks I & II

Mod 338...Indicates strengthening fuselage at attachment of tail plane. Introduced on all Mks.

Mod 383...Indicates increased gauge of stern plating. Introduced on Mks I, II & V.

PeterA