The APF fitting is common as the Seven Workshop replacement headlamp unit uses it. However, the options for replacement bulbs are not great, should you wish to tinker; especially if you are sticking to 6V electrics. Getting to the bottom of specifications is not as easy as it should be, for this reason – there are three APF specifications:
They are easy to distinguish but identification just on their ‘APF’ description is impossible without further investigation.
The miniature Pre-Focus P15d/3 appears to be a 26mm flange, in comparison to the P15d/1 (the fitting Austin replacement units use) of 30mm.
Things are further confused as P15d (Europe) are also listed as P30d in America…
You have been warned! This site has some further measurements.
Classic Dynamo and Regulator Conversions has LED light bulbs and bespoke boards which have been well used for a number of years and their site is very informative. You can also find APF bulbs direct from China through places like AliExpress; cheaper – but with more risk!
Can anyone add anything to this post?