Three point hitches

Technique: Three point hitches

Parts:	Frames, Nuts, Bolts, End caps, Plates
Techniques:	Tri joints, Space frames, Trusses, Bolting

Introduction

The three-point hitch is a widely used type of hitch for attaching ploughs and other implements to an agricultural or industrial tractor. The three points resemble either a triangle, or the letter A. Three-point attachment is the simplest and the only statically determinate way of joining two bodies in engineering.

Challenges

Build hitches to meet industry standard sizes using parts and as few vitamins as possible.

Size categories

There are five different hitch sizes, called categories. The higher category hitches have sturdier lift arms and larger connector pins.

Category	Tractor power	Top link pin diameter*	Lift arm pin diameter	Lower hitch spacing
0	Up to 20hp	5/8 in	5/8 in	20 in
1	20 to 45hp	3/4 in	7/8 in	28 in
2	40 to 100hp	1 in	1+1/8 in	34 in
3	80 to 225hp	1+1/4 in	1+7/16 in	40 in
4	More than 180hp	1+3/4 in	2 in	48 in

There are also variants to the above categories denoted by N, (narrow). These utilize the pin sizes of the listed category, but the width of a category one step lower. The N variations are common in "quick hitches" and allow larger tractors to easily hook onto smaller utility implements.

* refers to implement end; tractor end not specified

Approaches

• 

  Plate adapts to 5/8 inch, 3/4 inch, 7/8 inch pins for category 0 and 1

• 

  Category 0 hitch

References

• Wikipedia: Three-point hitch