Spicer IPL: Tandem Drive Axle Illustrated Parts List - All Non-Current Models - Manual (Page 33)

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Differential Carrier Identification
Axle Model Nos.
Differential carrier identification is either stamped on the carrier itself or
on a metal tag affixed to the carrier. Location on the carrier is the same.
For 440 Series Tandems, use 440 in place of 460.
For 480 Series Tandems, use 480 in place of 460.
For 550 Series Tandems, use 550 in place of 460.
For 580 Series Tandems, use 580 in place of 460.
For 650 Series Tandems, use 650 in place of 460.
Spicer identifies a tandem axle
by the nomenclature assigned
to the forward axle.