No 4 Mk 1 rear sights

Question regarding manufacturers of Mk 1 rear sights for the No 4.
I have one marked with small F on rear face and again on top of elevation winder, and another (fitted to my 41 Matby) marked on left side RFI CR318, with RFI on top of winder - (I know its not orig as I fitted it myself after getting the rifle from my father)
Are those with the wisdom able to tell me who made these Mk 1 sights please

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Originally Posted by brnom2

Question regarding manufacturers of Mk 1 rear sights for the No 4.
I have one marked with small F on rear face and again on top of elevation winder, and another (fitted to my 41 Matby) marked on left side RFI CR318, with RFI on top of winder - (I know its not orig as I fitted it myself after getting the rifle from my father)
Are those with the wisdom able to tell me who made these Mk 1 sights please

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F indicates Fazakerley manufacture, RFI is Rifle Factory Ishapore.

Thankyou birdhound