And that had a wall thickness of .043.

You insert it from the front of the bolt and engage the bolt notches.

Then turn it to unscrew the firing pin, which will then come out with the firing pin spring around it.

Here's a picture of the old spring (top) compared to the new spring (bottom).

You then install everything in reverse order.

You will be able to feel the much stronger spring when you close the bolt, as Lee Enfields cock on closing.