So, what is the "Special Ring Device" or "SRD" anyway?
Simply, the SRD is a device made up of two metal rings that lets you take up slack in a piece of rope.
A piece of rope is fed through two steel rings in such a way that friction causes the rope to slide in one direction but not the other. The device is most commonly used by self-bondage enthusiasts to perform strict bondage scenarios that would otherwise be very difficult if not impossible without a partner. A very tight hogtie can, for example, be accomplished by attaching the SRD between bound feet and hands. When the SRD is pulled taught, the hands and feet are drawn together.
To use the SRD, you'll need two welded metal rings and two lengths of rope. I've
found that rings with an outer diameter of two inches works well with 3/4" nylon rope.
If you use a different size rope, then you may need to experiment with different ring sizes.
I've found that the effectiveness of the device decreases as the diameter of the
ring increases in comparison to the thickness of the rope. For example, if you
are using 1/4 inch rope, you might find that the device slips with the two inch rings.
Switching to one inch rings should solve the problem.
The first step is to tie the rings together using one of your ropes. The other end of this rope should be tied to your anchor point. In the case of the hogtie example, you would tie the rings to your feet.
Feed the second rope through the rings from the back.
Next, feed the rope over the top of the front ring and through the back ring.
Feed the rope a second time through the back ring from front to back. When you pull on the "short" end of the second rope, it will slip through the rings. When you pull on the "long" end, it will not move.
Going back to the hogtie example, if you tie the “long†end of this rope to your hands and pull on the "short" end, your feet will be drawn towards your hands, but you will not be able to pull them away.