totally confused (light bulbs) - not now but

In my quest to track down 'better' stop/tail & indicator bulbs I've lost the plot. Are these a BA15d/15s fitting or BAY15d/15s. I know the difference between BA and BAY but I can push either fitting into my lights - I would have expected one of them to have 'popped' out but both fittings are quite firm (or is it that Lucas made the lights so they would take either fitting)? Yes I'm going to see my sparky tomorrow but I thought I'd ask MGEsters. AFAIK these are original receptacles from 1966 - my front indicator/park housing has Lucas stamped on it.


Well it helps if one's test bulb is a complete bulb. half a pin was missing from the BAY15d I was using. Once keen eyes pointed this out I got the 'popping' I anticipated. I can't thank anyone for their help but so I just posted this for the record. BA15s for indicators BAY15d for tailight/stoplight.

bump

bump - see edit to OP (if interested)

Should be BAY15d/15s to make sure the correct element lights at the proper time.
If they both fit someone forced the BA15d/15s at one time or another.

Correct bulb for '66 front indicator is bulb 1073