VBA Inputbox to Prevent Decimals

I am trying to develop a tool that will help standardize a description catalog of products. I want to have an input box prompt a user to enter a size. I want to encourage size entries like "5-1/2" and prevent users from entering "5.5". Ideally, if the size was entered with a decimal and not a dash with a fraction, I want a message box to pop up saying they can not do that. It would then need to re-show the input box.

Here is what I have -

Private Sub CS_Other_Click()
Unload Me
Sheets("Fill In").Activate
Worksheets("Fill In").Range("C2").NumberFormat = "@"
Dim other_casing_size As Variant
other_casing_size = InputBox("Fill in the casing size. Syntax MUST be in the form of X-X/X", "New Casing Size")
Range("C2") = other_casing_size

I just dont know the code to prevent an entry with decimals. Even better, if i knew how to code an exact syntax to include or exclude anything I wanted that would be perfect.

Thanks