From parallel waves (right- or left-hand) or eight chain thru formation: Ends and adjacent dancer (neighbors) arm turn half, new centers in the wave arm turn 3/4 to form a wave across the center of the set. Centers of this wave now trade (half arm turn) and then arm turn the end of this same wave 3/4. Finishes in parallel waves. If started from eight chain thru formation, the first half arm turn is by the right. If you want dancers to start with a left arm turn from eight chain thru formation then you must give the call as Left Spin Chain Thru. BACKGROUND NOTE: Spin Chain Thru stands at the head of a very large family of movements that somehow involve dancers who move from one wave to the other by going through the middle of the set. Actually the basic idea was originated by Deuce Williams from Dearborn, Michigan who invented a move called Swing Chain Thru in 1967. Swing Chain Thru used one-quarter arm turn (hinges) in the places that Spin Chain Thru uses three-quarter arm turns; and in 1967 the one-quarter turns were deemed not as comfortable as 3/4 turns, so it was Spin Chain Thru that caught on generally while Swing Chain Thru received more limited use.
Rod Blaylock 1967
This definition is from The Handbook of Modern Square Dancing by Jay King.
It is provided here for informational and educational purposes only.