Syntax to add a number to an evaluated part

Hello,

This is my first post in this forum and I still consider myself as a rookie in solidworks.

I am trying to add a material thickness of .25in to OD to obtain RAW OD (5.75).

I tried "D8@Sketch1@P01-00212-A.SLDPRT"+.25 but it didnt help.

Any suggestions?

Thank you!

SolidworksBill Of Materials