159 or 501 Base Fuze?

[MRoy]

I Need some help to identify this british fuze. Markings suggest it could be a 159 or a 501 but they have same dimensions.
How to make the difference between them?

 

[Rrickoshae]

501 mk1 naval. The 159 is probably the lot number

 

[LEAFLET]

Hi Roy,
Like Rrickoshae said it's a No 501 Mk I.
The base looks different (see Pictures)
LEAFLET

 

[Alan1]

Here's the 501 mk 1 N in section.
Alan1

 

[MRoy]

Thanks very much at all for your answers, that help me a lot.

 

[Daffodil]

And another.