UKC

Evening question for you lovely people.

I need to replace a few G4 halogen capsule bulbs but they seem to come in a range of M numbers. M91, M86, M32 and M11 all seem to come up but they look identical.

Any idea what the M number means? Google, for a change, hasn't helped (or I'm asking the wrong question!)

Many thanks.

I think the M number refers to the filament type/size /arrangement and capsule shape (and possibly material). For general purpose lighting uses this simply doesn't matter but for use in things like projectors it does. So if this is used for lighting you can ignore it  and just go for G4 (fitting) and wattage.

You might need to be careful if you replace halogen with LED you may need a new transformer.  

Are any of these what you need? 

https://www.screwfix.com/c/electrical-lighting/light-bulbs/cat8350001?capfi...

https://www.screwfix.com/c/electrical-lighting/light-bulbs/cat8350001?capfi...

Is it G4 or GU 4

GU4 is the same fitting as M11 

Definitely G4. You're right. It probably doesn't matter that much.

The trouble is that I hate not knowing something once I know that I don't know...

Don't worry about the known unknowns. It's the unknown unknowns that will get you.