One of my favorite machining touches - on a comparatively ordinary mid-range model, the pre-war Diana 27.
1. Top of the breech block is cylindrical, on a larger diameter concentric with the round barrel.
2. This contour makes a straight line where it meets the flat sides of the block.
3. The top of the breech forks have neat narrow horizontal flats that exactly meet the same line; a neat and lovely styling detail that continued onto the first generations of the post-war, ball-sear model 27.