Kerry Zeiler (who recently passed away) was a former radiologist-turned-cuemaker that was given access to a large collection of the most famous maker's cues to x-ray many years ago. He would not reveal their "secrets", but began to build cues that played amazingly well, supposedly using some of this, some of that, and lots of Kerry. RIP Kerry, you were truly an artist.
Somebody was fortunate enough to have seen those x-rays and have Kerry explain to him what he saw. Kerry took some of those cues from the old Best Billiards then across the street where he would X-ray them.
From those x-rays and testing the cues that really interested him, he came up with his butt taper and A-joint configuration.
The late Edwin Reyes also had a collection of x-rays. So extensive he actually made a spreadsheet of their pins, A-joint studs, diameters , buttcaps etc in diameters and lengths.