The inner washer question...

[Whizbang]

I am new to replacing SR scales...but I want to get better. I have several nice old blades that need new scales. I have not done a lot of scale replacements. The few I have done on antique razors were because the scales were cracked or broken but the blade was still in very good shape. I noticed that when I remove the old scales some, but not all of the razors have an inner washer (thin plastic or brass) on the inside of the scales next to the tang. If you were putting on news scales on an old blade would you use inner washers or not? And what is your rationale for this decision? And if you do use washers what size do you use? I've been looking online and can't find anything about the proper size for inner and outer washers.