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Q1: what are the specifications for a replacement axle for a 2004 Karavan Trailer, model number BW-1700-70 so that I could just order a new axle from a local trailer shop and not have to drive two hours to measure the axle myself?

BACKSTORY
This trailer was the original trailer provided for my son's 2004 15-foot Boston Whaler boat.

Some original paperwork has a part number of 310-01521, but that is no longer valid. KARAVAN say the replacement axle number is 310-01572-zn, but they won't provide any specifications.The can ship me the axle but the cost is very expensive and will take up to three weeks.

The boat is two-hours away.

I think a two hour drive will be your best-ever investment. I wouldn't depend on a reader of your post having the exact and accurate details of the axle that happens to be on the trailer under your unidentified model family of Boston Whaler boat.

It is not surprising that the trailer manufacturer won't give you all the specifications for the axle they are using. Typically a manufacturer of a product will want to sell you replacement parts. They are not in business to enable you to buy a replacement part from another provider.

A good source for trailer replacement parts is Eastern Marine Trailer Parts Superstore. See

https://www.easternmarine.com/

They might be able to help you. See

https://www.easternmarine.com/karavan-trailer-axles

They list 17 different KARAVAN trailer axles available.