There had been a lobbing sight that was missing and I found that I wasn't able to see the open sights clearly enough to contemplate using them and not wanting to (spend money) use an off the shelf aperture, I decided to make one. If I came across a bolt mounted unit I may change but for now this will work handily.
First I needed a fitted backing washer to bring the lobbing sight recess out level with the wrist

An alloy pattern and a length of steel came next

The top of an old jack supplied something to hold the aperture and an un-used ruger ring knurled knob would become the aperture itself.