Algunos comentarios de los foros americanos:
http://g838.org/viewtopic.php?f=2&t=3004otros foros
..........Usually only 3/4 ton trucks and above had the plate. Perhaps (notice I won't say "never", etc.) airborne units would attach a plate to a jeep just to ease rapid loadout on aircraft, etc. But not an army requirement that I'm aware of.
............ The weight plates were required for the 3/4 ton series trucks and up, and not on the 1/4 ton truck. However there is a clause providing that they may be used optionally at "local commander option" so this may explain why a few are seen with them but it certainly wasn't common. For all intents an purposes it was not done, but there were exceptions.
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Some Common Bridge Plate Numbers
Light Trucks 4
Reconnaissance Trucks & Jeeps ......... 2
Trucks 2.5 - 5 ton ..........................10
Trucks 5+ ton ...............................21
Stuart Tank ..................................19
Sherman Tank ...............................30
Hellcat TD ...................................18
M3 Half-Track ...............................10
.......By the early 1960s the fractional display of tow vehicle over trailer changed. The tow vehicle displayed the combined bridge class of vehicle & trailer denoted by a large "C"