windshield channel width?

I've been working on a roadster over the last year or so. Some day I'll post some pics. I'm to the point where I would like to start working on the windshield posts. One problem though, I can't seam to find out how wide I need to make the channel for the glass and rubber to fit into. Anyone got the right dimension for 1/4 glass?

Thanks

 

come on...... no one knows how wide it should be to hold the rubber and glass

BTTT

 

1/4" plus gasket material. That appears to range from 1/64 to 1/16