Hope you can get your heads around the drawing. The whole unit of course fits into the cocking lever tube which I have left out for clarity. The little pin which is about 2.8 mm dia holds the whole unit in place by sticking through the top side of the cocking lever. The wire ring must be able to fit into the notch of the locking lug on the barrel. The stop washer slides down into the cocking lever until it hits a ledge where it sits to hold the spring. The plastic sleeve slides on the main body to hold the wire ring in place against the machined shoulder on the body. You can work out all your dimensions from the cocking lever.

Baz

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