Are you entering data into the TextBox and it changes to a date? Or entering data in a cell and it changes to a date?
If TextBox:
Anything typed into a textbox will be interpreted as text. The only way for this to happen is if your code changes it. Do you have any subs for events for the TextBox? Please show your UserForm code.
If cells:
Are you doing calculations on the sizes or just using them as text? If you just need them as text, then format the column as "Text" and it will take whatever you type in without trying to convert it. If you need to do calculations, then you need format the column as "Fraction" and when you type 7/16 it will display 7/16 and hold 0.4375 as the underlying value. But then you can't search on "7/16". Your search code would have to be changed to look at the .Text property of the cells instead of doing a .Find or whatever you are doing. Please show your UserForm code.