The Bren gun was made to metric standards and threads due to licensing agreements. The wood was finished in linseed oilicon only. Before you start to assemble your Bren Gun, you ought to find a local metal finishing company locally and have all of the parts bead blasted and chemically blackened. If you do not do this, you will soon see that it looks bad and in a year or so, you will strip it all down again and do it properly. To make it look like a correct skeletonised gun (that is what the SKN stands for.....) you should paint the edges of the cut away sections in red.

Before you screw the return spring tube into the butt slide (the lower section) please come back and I will tell you the CORRECT way to do this.