Something of a minefield Nick but hope this clears up the Lucas variants available:
L794 single filament/contact BA15s base
L795/L691 double filament/contact BAY15d base (usually supplied with lens and integral reflector)
To which can be fitted the following lens available in clear, red and amber:
L691 series lens with pointed shape
L794/5 series lens, deeper flatter front which accomodates integral reflector requiring longer screws
FWIW my Roadster and other trads 2014 onwards standard spec ex factory uses:
L794 front base and lens in amber for indicator
L794 rear base with L691 amber lens for indicator
L795/L691 rear base with L691 red lens for stop/tail
If you need to change lens screws for stainless maybe, the thread is 6-32 UNC.
For completeness the Cobra brake repeater on trads employs the smaller diameter L760 base and lens with the latter available in red or clear.
Not confirmed but the Cobra re-introduced on latest CX models appears to use same diameter as other rear lamps.
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