What model is my grandpa sitting on?

[laurensberends]

Hello everybody,
My name is Laurens and I'm from the Netherlands. I'm a motorcycle enthusiast and currently rebuilding a BMW r100r into a cafe racer style custom for a friend.
Today I found a old picture of my grandpa on his motorcycle. Since I'm not owning a motorcycle at this moment I maybe want to look for the one my grandpa owned. I can't find the exact model so I hope you can help me. The only thing I've got is this old picture. For what I can see using Wikipedia I think it's a model from the 30s, maybe a M23?
Thanks a lot, greetings from the Netherlands

[JulianS]

Not a BSA I think a Triumph 3H 350cc from the 1930s.

https://www.google.com/search?q=triumph+3h+motorcycle&tbm=isch&ved=2ahUKEwiAvMaejtbtAhUSTBoKHaiaBWoQ2-cCegQIABAA&oq=triumph+3h+motorcycle&gs_lcp=CgNpb

[arturro]

In my opinion this is Triumph 3HW 350cc please look at rear carrier (rack) Front lamp is also the same for War Departament models. Ather the war this bike was adopted from WD to civil.

https://www.handh.co.uk/auction/lot/149-1944-triumph-3hw--350cc/?lot=51466
http://suprememotos.com/triumph/45477-wwii-triumph-3hw-rare-motorcycle-350cc-girder-fork-wd-ex-army-miilitary.html

Best regards Artur

[laurensberends]

Okay, thanks a lot. But why are the BSA and the Triumph so similar?
Do they share the same engine but only with other covers?

Greetings

[Rupert]

Same designer, Val Page... hence similar look but nothing interchangeable. Also did the Ariel Singles to the same basic design.