I have now also purchased a John Knibbs washer set and can confirm the screw is a perfect fit so very happy that i can finaly put my rifle together. JK screw is protruding in front of the leather washer so i am worried it might be slamming in the back of the transfer hole. Metal to metal contact cant be good but i might be wrong. I might reduce the insert leather washer or use the chambers main leathe seal with JohnK other bits in which case i got a perfect fit. Couldnt agree more, and i am also very very grateful that these parts are still available for my 104 years old air rifle absolutely amazing. Will purchase few JK spares just in case at the same time still think Chambers clearly selling the wrong screw is disappointing as if this is the missing part you will not be able to put your rifle back together. Tx for the links much appreciated JK as you say is very good value for money no doubt about that.