Front wheel bearings - how to identify axle type?

[camrycurt]

I want to get new front wheel bearings for my 1970 C10, but the NAPA site lists two different products depending on the axle type on the truck and I'm not sure how to figure out what axle I've got. Can someone please tell me how to identify which front wheel bearings I should get?

Here are the choices from NAPA, which appear to be SKF bearings because the part numbers are the same:

Part Number: BRG BR2
Product Line: NAPA Bearings
IMPORTANT INFO: w/ IFS25 Axle

Part Number: BRG BR3
Product Line: NAPA Bearings
IMPORTANT INFO: w/ IFS30 & IFS35 Axles

How can I tell if I have an IFS25 axle or an IFS30/IFS35 axle?

Thanks for the help!