# Human diode **URL:** \ **Category:** In My Humble Opinion\ **Created:** [February 16, 2010, 4:29am UTC](https://boards.straightdope.com/t/human-diode/529168 "2010-02-16T04:29:24Z")\ **Posts on this page:** 2\ **Page:** 2
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [February 17, 2010, 1:39pm UTC](https://boards.straightdope.com/t/human-diode/529168/21 "2010-02-17T13:39:20Z")
> [@CalMeacham](#): > > … there are “turnstiles” that consist of revolving-door-type constructions that run from floor to ceiling, but instead of glass panels they have a “wall” of rigid horizontal rods connected to the central rotating post, forming a plane. Like [this](http://turnstile.perco.ru/img/catalog/RTD-15big.jpg) ---
**Author:** ![tdn](https://avatars.discourse-cdn.com/v4/letter/t/94ad74/32.png) [@tdn](https://boards.straightdope.com/u/tdn)\ **Post date:** [February 17, 2010, 4:08pm UTC](https://boards.straightdope.com/t/human-diode/529168/22 "2010-02-17T16:08:59Z")
> [@CalMeacham](#): > > They have this at subway stations here in Boston, at the zoo, and at the doors of two companies I’ve worked at – there are “turnstiles” that consist of revolving-door-type constructions that run from floor to ceiling, but instead of glass panels they have a “wall” of rigid horizontal rods connected to the central rotating post, forming a plane. The center post can only rotate in one direction. You can go one way through the stile, but you can’t make it rotate to go the other way. And you can’t “follow” the stile around to go backwards because there is a “wall” of similar rigid pipes forming a stationary plane that blocks your progress. The rotating rods can pass through this stationary plane, however, because their bars interleave with the stationary ones. That’s a pretty long explanation for “meat grinder.” [Previous page](https://boards.straightdope.com/t/human-diode/529168.md?page=1)