Fith wheel or fiver?

So I was reasontley asked by a truck driver friend why I call our RV a 5er and not a 5th Wheel? 

To answer this question lets talk a little about the various ways one can connect a trailer to a truck.

1: There are trailers that connect thru a Receiver Hitch often times in slang called a (bumper pull trailer). This type of trailer is connected by mounting a hitch underneath the vehicle that has a protruding end called a receiver that a ball is added to connect the trailers tongue to the tow vehicle. These Receivers Hitches are available in multiple sizes depending on the weight of you trailer. The size of this type of hitch is dictated by both the weight of the trailer and the vehicle pulling it. C

Usually this type of hitch are recognized as Class 1 thru Class 4 with weight ratings of 2000lb up to 10,000lb. respectively. 

Fifth wheel hitch

A Class 5 trailer hitch is mounted in the bed of pickup truck which uses a plate in the bed of the truck (similar to a semi-tractor) and a pin on the trailer.

Gooseneck

A Class 5 hitch also mounts in the bed of the truck but uses a ball in the bed of a pickup truck(either 2-5/16" or 3" in diameter) to engage a coupler on a trailer. Not to be confused with a fifth wheel.

The difference is a gooseneck trailer slides over a ball hitch in the bed of a pickup truck, while a fifth wheel trailer attaches to a pickup truck using a hinged plate hitch; the same type of hitch is used by semi trucks. The biggest advantage of a gooseneck trailer over a bumper pull is its stability. 

Both the Fifth wheel and the Gooseneck hitches are made to pull up to 30,000lb loads. 

Hence I call my 5th wheel RV trailer a 5er. No to be correct I switch the pin box on the trailer to a air ride, shocked Goose Neck as the Dually we bought already had a Goose ball on it.