'join them together' is correct and usable in written English.
You can use it when referring to combining two or more objects or ideas into one. For example, "The two pieces of fabric were very different, but I was able to join them together to make a quilt."
Chemical crosslinking reactions between collagen molecules join them together - the nanosutures are the crosslinks themselves.
The amorous interchanges are carefully allocated to the individual groups, and there is no attempt to join them together until the very end.
All these individual pdfs will print out on A4 and you'll need to join them together to make the complete patterns.
MacCarthy, who saw the comedy and the philosophy separately at the Court theatre, thought it would be a mistake to join them together as a single stage drama.
The company actually had to erect two separate buildings, with plans to join them together later, because the litigation, a chronic problem in Indian real estate, delayed construction on the 30 percent of the site's acreage that was in question.
The characters don't aggressively seek out one another's company, but they don't need to hold hands to be connected; the dogs at their heels join them together, and magnify their attraction for one another.
Those selected will then wear a long wig that joins them together.
But no one has yet joined them together on an industrial scale.
The choice is now between Kmart and Prada, and the institutions that joined them together are finished.
In proportioning the mix, the aggregates are graded in size so the cement matrix that joins them together is minimized.
His great innovation was to assemble the elements of his simple, linear sculptures on the floor, without joining them together.
