Do I detect that your issue is with not being able to see the sight diagram (The black bull area) very well, and the suggestion to you was that something to magnify the diagram may help?
If I am correct, you may be wanting what is now called a sight correction lens, or as we used to say a magnifier' on the rear sight. These are products that you can 'zoom' in and out to improve your sight picture (If you know what I mean)
As Tim says, the choices of what you can get in a rear sight screw in eyepiece are endless, and you need to know exactly what product you are wanting, or you will end up with something you did'nt want.
Did you know, there are more people live in Yorkshire than there are in Scotland! Viva la Yorkie Home Rule. Me an Ms Sturgean have a plan.
You South Yorks heathens will need to apply for a Special Dispensation when Wakefield becomes the new London.