A humbler is a BDSM physical restraint device used to restrict movement of a submissive male participant in a BDSM scene - mostly involving cock and ball torture. - Wikipedia 

This devious CBT device consists of a ball stretcher/cuffs which restricts around the base of scrotum, assembled into a solid wooden or acrylic bar passing. The bar passes behind the thighs at the base of the buttocks - which restricts movements of the wearer. This sex toy forces the submissive to keep his legs folded forward, it is not possible to stand upright as any movement to straighten legs pulls hard on the testicles. The pull will follow with extreme discomfort or pain.

As you understood, the humbler will keep a sub on all four! It is quite easy to install, but not a simple task to stand on his feet. Simply open both parts of the bar and clamp it back in place with scrotum stuck and restricted. Open and close the device with the provided screws and make sure the humbler passes behind the thighs. 

Once the submissive is on his knees and the humbler sex toy is tighten up, CBT session and humiliation play can begin. The humbler is stretching the slave's balls all the time, leaving the penis and testicules exposed to any kind of torment. Combien it with ball busting, electric play or any impact toy and your slave will only beg for more. 

To assert dominance by a mistress, pulling up the device will directly assert the slave into submission.

Any experienced dominatrix will know how to put the device easily into the scrotum. Once the slave is secured and on all four, with his balls exposed, it is when the real fun begins. There are multiple cock torture scenario on how a humbler can be used:

Your imagination is the limit. But remember to play safe and always use a safe word.

Usually made of wood, they can also come in Acrylic or Steel versions. Some CBT humblers are combined with other CBT devices which add some fun to the play. 

For an even more restrictive experience, it is possible to combine with ankle restraints cuffs attached to the extremities of the bar - This is called a balls to wrist humbler.

This fully adjustable testicle cuff was created for the purpose to make men totally obedient. The bar is restricting movements which is a powerful power exchange mechanism and the balls being pulled constantly reminds the slave’s vulnerability. 

The humbler enforcer is to easily control a submissive while him being in a humble position and then incorporate cock and ball torture into play. 

Using a humbler is not only for ball torture as one might think. It is perfect for submissive training, as the restricted movement and the pain associated forces slaves into total obedience. In a femdom relationship, there are power exchanges involved, which sometimes translate into physical pain to get what the dominant wants.

How does the Humbler force the wearer into a kneeling position and create discomfort when attempting to straighten the legs?

The Humbler is designed to be secured behind the thighs at the base of the buttocks. This positioning forces the wearer into a kneeling stance by making it difficult for them to straighten their legs. When any attempt is made to straighten the legs even slightly, the device exerts pressure directly on the scrotum. This results in significant discomfort, effectively discouraging the wearer from attempting to adjust their position or stand upright.

What materials is the Humbler made of, and what are its dimensions?

At Oxy, we offer few options:

• The Wooden Humbler is designed as a testicle cuff device meant to restrict a man's movement effectively. The wooden Humbler securely fastens around the base of the scrotum and is positioned behind the thighs at the base of the buttocks.
  
  
• Acrylic Humbler will keep him on his knees, for sure.
  
  
• TNG Humbler & Ball stretcher is a 2-in-1 universal CBT toy made out of Stainless Steel. U-hoop goes over your partner's or your balls. For additional fun, you can attach a weight or whatever else you use to play with. 

Full vulnerability to your dominant by staying in a humiliating posture. The pain and discomfort associated is what makes one of the best CBT devices out there. The deviant device immobilises, tortures the testicules, which will make you obey your master.

Story told by Mistress Elena, owning an acrylic OXY Humbler: 

Every time I use it, I think to myself that it is one of the best CBT toys ever invented. The enforcer acrylic humbler is soft to the touch, yet devious in its use. The sleek curve fits my slave ass to the perfection as it restricts his scrotum and movements. 

“Come” I gently whisper to him, smiling at the irony of that one word. He crawls over and stays at my feet, in the apprehension of what is going to happen next. “Turn around”, he obeys and I push him into the ground with one leg, until his face touches the floor. I am now seeing his soft bum and his hanging testicles. 

“If you keep being a good slave, this won’t be a big punishment”. He mumbles. I grab the humbler, place his balls into the humbler’s hole and screw the device back together. “Stay on your knees and follow me”, i slowly walk away while he moans in discomfort “Since you are all set up, let’s play a bit more” - Taking the anal spreader out of my dungeon chest.

As with any BDSM toy, especially involving cock and ball torure, you must remain vigilant of any long term damages caused to the penis or testicles. The biggest danger is circulation blockage. Any binding is too tight if it cust and causes bleeding. 

The cock and balls normally become engorged with blood during sexual arousal, turning reddish or purplish as a result, and up to a point genital bondage just helps that process along. Circulation could be dangerously impaired by tight bindings before there's much loss of color. 

A good rule of thumb is to loosen tight genital bindings enough to restore full circulation every 20 to 30 minutes even without any signs of a problem. And in no case should anything tighter than a comfortable ring or harness be left in place overnight or throughout an extended scene. 

Dirk Stein David - Cock Torture Health and Safety