Use Any Width Beam for Swing Set
Use Any Width Beam

Tools List
The 3 minute video above explains the option of making a composite beam from easy-to-find 2x6 lumber. There are reasons why you might prefer a composite beam.
1. Use Any Width Beam
These brackets fit any width beam. The beam must be 5 1/2" high in order to fit the brackets, but the other dimension of the beam--the width--does not matter.
2. Increase the Weight Limit
The typical 4x6 beam is sufficient for most applications, but if you would like to design a swing set with a higher weight capacity, you can use a wider beam. The beam is the deciding factor on the weight capacity of a swing set--the brackets and legs can hold so much more. You can opt for a 6x6 (5 1/2" x 5 1/2") beam, or make a composite beam out of three or four 2x6 boards.
3. 4x6 Sometimes Hard to Find
Decent 4x6 lumber can sometimes be hard to find in today's market. One option you have is to make a composite beam of three or four 2x6 boards, as explained in the video above. If you do decide to use a composite beam, there can be some advantages. First, you usually have a wide selection at the store of good 2x6 lumber which means it not only is easier to find but you can pick nicer lumber sometimes. Second, a composite beam does not twist or crack much over time like a 4x6 beam can. Having said this, for most people the typical 4x6 beam is probably the best route, but sometimes the composite beam might give you the options you need.