I put a new barrel on a Mauser and since it is different dimensions from the original I thought I would call williams and ask what combination to use with measurments I had. All I got was well just look at the web site and you should be able to figure it out. i told Steve, customer service?, that i had looked and the web site directed me to call for service. Well we left it with i could just go buy some various sizes and see what combination's would work. I could not even get the sizes of the sights out of the guy. Some customer service. Needless to say I will not be using any Williams sights in the future.