The following info is supplied by Vortech, although it does not seem to be available on their web site, it is printed on the back of a Vortech spinners package.

Engine Manuf. Engine size  Crankshaft thread
Como .19 - .61 Imp 1/4 - 28
  .75 - .90 Imp 5/16 - 24
Enya .15 - .25 M6 (6.0 x 1.0mm)
  .25 - .53 Imp 1/4 - 28
 

.35 - .60, .60 - 1.2 4-Stroke

 (non R engines)

7.0 x 1.0mm
  1.2R 4-Stroke 8.0 x 1.0mm
Fox .19 - .50 Imp 1/4 - 28
  .60 - 1.20 Imp 5/16 - 24
HP .21 - .61 Imp 1/4 - 28
  1.20  4-Stroke Imp 5/16 - 24 (or 8.0 x 1.0mm - conflicting data)
Irvine .20 - .61 Imp 1/4 - 28
K&B .16 - .65 Imp 1/4 - 28
OPS .40 - .60 Imp 1/4 - 28
  Maxi .30 M8 (8.0 x 1.25mm)
  Super .60, .61 5-port 8.0 x 1.0mm
  .65 M6 (6.0 x 1.0mm)
OS .25 - .60 Imp 1/4 - 28
  .61 - .90 Imp 5/16 - 24
Peco .21 - .45 Imp 1/4 - 28
  .60 - .80 M8 (8.0 x 1.25mm)
Rossi .40 - .61 M8 (8.0 x 1.25mm)
Saito .30 - .45 M6 (6.0 x 1.0mm)
ST .25 - .60 Imp 1/4 - 28
  .61 - .90 Imp 5/16 - 24
Webra .28 - .80 Imp 1/4 - 28
  .61 - 1.20 M8 (8.0 x 1.25mm)
YS All 2-Stroke M8 (8.0 x 1.25mm)
  .90 - 1.20 4-Stroke 8.0 x 1.0mm

Unless states otherwise, all engines are 2-strokes.