Mariano, the two groove pumps (37 to 48) are bearinged (high load) pumps the single groove (sheave) pumps are only bushed. There are a lot of different front pulleys, fan locations, high output generators, big fans (requiring high torque loads) which require tighter belts etc.
Cars often only used the single sheave pump because the fan was driven by a separate belt, so the generator and water pumps only had a single sheave. (the load was less) There are many variations. Btw the double sheave pumps also come in two different belt widths.
Does that help?
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Bluebell
Carrier Armoured O.P. No1 Mk3 W. T84991
Carrier Bren No2.Mk.I. NewZealand Railways. NZR.6.
Dodge WC55. 37mm Gun Motor Carriage M6
Jeep Mb #135668
So many questions....
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