Okay, so I have a love / hate thing about people that drive with fog lights on. Yes, it can look good and looks more complete with them on. But some of them cause immense glare and I even see some idiots drive in total darkness with fog lights on, but dipped beams off! Anyway. rant over, I wanted fogs and I wanted them to be purely aesthetic so they didn't cause glare and Plod wouldn't be able to tell me off.
I could have just bought H3 LED bulbs, but that would have cost me 12quid for UK ones and then if the colour temperature wasn't to my liking, I would be a bit stuffed.
I had a spare set of 501 bulb holders from the normal BA sidelights, so I made them fit, and its quite easy and works very well.
1. This is the normal 501 holder, we need to cut a few bits off and make some cut outs so it fits into the H3 holder properly.
[img]https://lh5.googleusercontent.com/_kmwYjBvt_Ac/TVxnS18VADI/AAAAAAAAA2o/rrXLOoOpQBg/s720/2%20the%20501%20holder%20from%20sidelight.JPG[/img]
2. This is the H3 holder
[img]https://lh5.googleusercontent.com/_kmwYjBvt_Ac/TVxnTA1UunI/AAAAAAAAA2s/nDspFygxvHY/s720/1%20how%20the%20H3%20socket%20looks.JPG[/img]
3. This is what I did. Cut the side notch things off, and make a cut out on equal sides of the disk shaped bit. Also, pretty obvious but remove the sealing ring, it isn't needed and will get in the way.
[img]https://lh6.googleusercontent.com/_kmwYjBvt_Ac/TVxnR38qJhI/AAAAAAAAA2c/TQ3yfpzo9QU/s720/4%20what%20the%20501%20holder%20looks%20like%20now.JPG[/img]
4. Snug

And it sits down perfectly level. I forgot to put the clip over when I took the pic - it DOES fit over perfectly just like a normal H3 bulb. You may need to fiddle with the clip to get it properly secure but it works.
[img]https://lh3.googleusercontent.com/_kmwYjBvt_Ac/TVxnSTk51uI/AAAAAAAAA2g/7w9Nq0Zbqyo/s512/3%20modded%20501%20holder%20in%20h3%20socket.jpg[/img]
5. Here you can see the bulb and holder clear the casing perfectly, so no light output is lost. Only had a normal bulb to hand when doing this, but see my car's thread for pics with a 5 SMD LED in place (the type with LEDs on all sides, not just forward facing).
[img]https://lh5.googleusercontent.com/_kmwYjBvt_Ac/TVxreRP3LAI/AAAAAAAAA3o/DF94PfD7Np0/s720/6%20modded%20501%20clearance%20inside.jpg[/img]
Result!
[img]https://lh3.googleusercontent.com/_kmwYjBvt_Ac/TVxnSqpkzfI/AAAAAAAAA2k/NeQ-RKb5J-4/s720/5%20result.JPG[/img]
Now you can fit whatever 501 bulb you like, although some of the longer LED bulbs may require you to take the glass off and remove the reflective thing.
You might also want to remove the tell tale bulb from your instrument cluster so you don't have a bright green light inside the car glaring at you. If plod does stop you - ask them to turn the fog lights on on there car to compare brightness. No way in hell you could cause glare with a standard kind of size 501.