70’s BSA bottom bracket size

[H12rpo]

right then just stripped out the BB from the 70’s BSA Prima and cleaned and degreased. The cups look ok and the axle tidy enough but Might as well replace the caged bearings I’m thinking before assembly ......however, there’s no identifying mark to say what size they are....anyone help with that please?
Cheers
Edit NERVAR 121 is stamped on the axle

 

[rogerzilla]

Normally 1/4".

 

[H12rpo]

Excellent thanks mate. Just ordered some

 

[H12rpo]

I don’t have one of those plastic dust sleeves. (The axle etc was removed by someone else so I don’t know whether there was one and they binned it) . Does it need one? And if so where can I source one? Already looked on the bay.
Tia

 

[midlife]

Only time I used sleeves was when the BB was cut out ( see avatar). There would not have been one when it left the factory. What bearings did you go for?

 

[H12rpo]

Oh right! I assumed they would be always fitted to stop all the loose dirt from the down tubes getting on the axle and races ???
I bought some 1/4 inch loose bearings ........I’ll put 11 in each cup.