You don't want to use the bolt-on allen-head skewers sold in bike shops. On a tandem they aren't sufficient and they typically are only 130 mm or 120 mm, while you likely have a 135 mm rear spacing.
Swap the entire axle out. You can do this with Phil Woods, Chris King, and any axle with a solid steel 10 mm axle.
Compared to those cheap bolt-on skewers, you'll have better luck with a stronger skewer. The Dura Ace are usually the strongest I've found and have worked well on many tandems I've ridden. Expensive but worth it.
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