Quick question about steering coupler

[tehzack1]

Hey guys, I've got a series 2 '55 Chevy truck. It's been somewhat updated with a 69 camaro front clip. I'm putting a tilt column out of a '92 G20 van with a cable shift as opposed to the linkage on the older van columns. I'm in the mounting stage right now with the column and i'm trying to figure out how to attach it to the quick ratio IROC Z steering box i've got on my truck. I've been doing a lot of searching on here and i'm reasonably sure that the input shaft on my steering box is 3/4" 30 spline. But my real question here is on the van output shaft on the column what is the measurement for the double D part? I've been looking at steering couplers and there is a 3/4 DD and a 1 inch DD. I measured my column and from the flat to flat side of the DD is 3/4". From the curve to curve part of the DD is 1". i'm sorta confused as to which measurement is used in determining which DD I have. Logic would lead me to believe that I have a 3/4" DD like the older van columns that i've read about on here, but I wanna be sure before I spend 65 bucks on a coupler. Thanks for any insight you guys can give.

[starterman99]

you want to measure the outer part of shaft or rounded side.3/4" DD shaft is 1/2" flat side measurement.sounds like you have 1" shaft size with DD.