The Chrysler mushroom: .970" foot. Why this size? Used on the Ford Model T - no, I'm not kidding, that's how old this is.
There's actual math to calculate the possible rate change: V = (tappet diameter - .040”) ÷ 114.6, where .040" is an acceptable safety margin to prevent edge contact.
Maximum values by tappet diameter in lift per degree of cam lobe rotation:
Engine Tappet OD Max velocity
Chev. Gen-3 L6, V8 .842” .00700”/deg.

Ford .875” .00729”/deg.

Chrysler, A.M.C. .904” .00754”/deg.

Oldsmobile V8 .921” .00769”/deg.

Model “T” mushroom .970” .00812”/deg.

Chev. Gen-2 235, 261 .990” .00829”/deg.

VW Type I• 31mm 1.220” .01030”/deg.