I get a great number of questions regarding cock and ball torture (CBT) and I am never quite sure how to answer them. While some men may thoroughly enjoy one type of CBT, another type might really put them off. Then there is the inherent danger. The penis and testicles (cock and balls) can be quite delicate. That is, they can be permanently damaged if you are not careful.
Having said that, let's take a look at a few things you can do as long as you take care NOT to over do any of them. That is, don't go to extremes. If in doubt, don't do it.
Weights: Adding weights to a man's balls in order to cause slight (or severe) pain is a common method of CBT. The easiest way to accomplish this is simply to wrap a thin rope or string (I like using round boot laces) around the ball sack just above the balls several times and tie it off. If you have enough string left at both ends you can tie them together forming a loop under the balls. To this loop, you can attach weights. Purchase your weights in the fishing aisle of your favorite department store. They come in many different sizes and can be attached to the string using Christmas tree ornament hooks.
There are a number of apparatus that can be purchased from just about any online sex shop to make this easier. But I don't recommend you spend a great deal of money on something you may discover you don't want to use. There are 'parachutes' that work well. They consist of a conical-shaped piece of leather with (usually) three chains that attach to a ring. These chains dangle below the balls and you attach your weights to the ring. Whatever you choose to do, PLEASE start out slow. Don't go adding a 25Lb weight your first time out. Start with something that only weighs a few ounces first.
Binding: Using the same string I described above, you can tie up your guy's jewels just about any way you like. You can get fancy by wrapping his penis from tip to base. You can make a fishnet type binding, or you can just tie a string to the tip and see how much weight he can “lift” when he gets really turned on. Of course you can always involve the balls when binding the penis. Just don't leave it on him all day unless you have tied him loosely (what fun would that be?). Anytime you start binding the cock and balls you risk cutting off the flow of blood. That can be dangerous. So limit the time you leave any bindings on.
Motor-Boat: This is a fun (for you, not so much him) thing to try. Wrap a string around his cock starting at the base and working your way to the tip. Don't tie either end to anything. Once you have him all wrapped up, take the end nearest the tip and pull it straight out from his body. It's like pulling the string to start a motor-boat, thus, the name. It's fun and reasonably harmless.
Electro-shock: This is my personal favorite. You can purchase (yes you have to buy something for this one) any number of types and styles of electro-shock devices. Most online sex toy stores carry a variety of them. By attaching the electrodes to various places on and around his genitals, you can achieve all sorts of results. Most devices have the capability to adjust the intensity of the shock and/or the waveform used. All I can tell you about this type of CBT is that it is FUN! Just make sure you ALWAYS turn down the settings before trying it in a new spot. (I learned that from experience.)
Then there are what are commonly called “sounds.” Sounds are long metal (usually surgical steel) rods that can be inserted into a guy's urethra. The name comes from using them like a tuning fork. The vibrations can be very stimulating. I recommend starting with the smallest one you can get. They do come in sets anywhere from four to twelve in a set. Always use plenty of lubrication when inserting ANYTHING into the penis. It will hurt enough, even with lubrication.
There are many other types of CBT as well. Try waxing the hair off his balls, applying some duct tape, or just sticking some regular tape to the hairy spots. Ripping it off is so much fun and fairly harmless. You can use any of a number of clips and clamps made especially for CBT (or nipples) but my favorite of these is that old standby... clothespins. I recommend the cheap ones because they have weaker springs.
I DO NOT recommend hitting, his balls with anything. Gentle slaps or finger thumps should be your limit. Serious injury can result from anything harder. He may be able to take the pain, but his genitals may not take the damage well.
CBT can be fun when you do it right. Just don't risk doing damage and you should be fine.