I'll try and take a wild shot in the dark, if I may ;-)
A Comet From Prime Portal Walkaround:
http://data3.primeportal.net/tanks/kam_wing_fung/comet/images/comet_100_of_211.jpg Looking at the image I would say that the handles are something
like half an inch in 1:1 scale, this would come out somewhere around
0.36 millimetres in 1:35, if we go for 0.4 mm we get 14 mm in real life,
while 0.3 mm gives 10.5 mm in real life.
A difference which isn't visible in 1:35 gives a span of nearly 4 mm in
real life. The paint you apply on those handles will probably result in
similar differences.
This one is also interesting:
http://data3.primeportal.net/tanks/kam_wing_fung/comet/images/comet_137_of_211.jpg My suggestion is to use something less than 0.5 mm and larger than 0.3
for the Cromwell and Comet.
The "main page" for the Comet is here:
http://www.primeportal.net/tanks/kam_wing_fung/comet/ A bunch of Shermans:
http://www.primeportal.net/apc/m4_sherman.htm a hatch on some M4A1:
http://data.primeportal.net/tanks/don_pics/m4a1/m4a1_39_of_82.jpg That handle seems to be somewhere around half an inch.
Same size of rod as for the Comet/Cromwell ....
Maybe half an inch was a readily available size of round stock steel when these tanks
were produced, if they had been built in a "metric" country I would guess at 10 or 15 mm
for real size. Imagine closing your hand around something and try thinking about a
comfortable thickness for the handle, not too thick but not so thin as too cut into your
hand when lifting something heavy and thick enough so that stepping on it or dropping
something heavy onto it will squash it and make it useless, ........ 12 to 15 mm???
In general: A model may sometimes need oversized details to make them visible or
allow the details to "survive", sometimes a detail should be left off since including it
as way too oversize would ruin the impression of the kit.
All of these fantastic reference images can be found at:
http://primeportal.net/the_battlefield.htm and to help with keeping this resource in existence:
http://www.primeportal.net/donate_money.htm / Robin (not affiliated with Prime Portal in any way)