Simon - I haven't got a bulb in front of me but I've used those reflectors before. Is there not a tang, albeit small, which determines? Don't know if this helps...
https://aus7in.wordpress.com/2015/10/27/...f-fitting/
I've recently found the motorcycle BPF reflectors which appeared cheaply on ebay WITH lens glass to be far better value, for those of us who aren't too worried about the originality of the glass.
https://aus7in.wordpress.com/2015/10/27/...f-fitting/
I've recently found the motorcycle BPF reflectors which appeared cheaply on ebay WITH lens glass to be far better value, for those of us who aren't too worried about the originality of the glass.