You know, doing weighted pull-ups or chin-ups using a backpack is not very comfortable and the weight distribution is far from being ideal. Thus people use dip belts for dips and pull-ups with weights. I was thinking if I should buy one or make one myself. The simplicity of the latter option outweighed the former one and I got to work!
I used a strong strap belt used for towing cars or strapping some loads on trucks. Okay, mine is not that strong, but it'll do for the time being. I just don't know how to call this kind of a belt.
At first I thought I would need some more things to make a usable dip belt, but it appeared that just a piece of the strap belt is enough! Just cut it with a knife or scissors to be suitable for your waist and to be not too long so weights wouldn't hit the floor on each of your dips.
You can just tie your dumbbells to it and use it right away!
On the second thought I decided to use my dumbbell plates which were lying around without use anyway, so I wouldn't need to bother attaching my dumbbells every time I wanted to do weighted pull-ups.
Again, just the belt may be enough if you make a sturdy and big enough knot on one end of the belt. The knot will not let the plates slip off the belt. A better idea is to reinforce the knot by some kind of a stick. It may be a bolt, or whatever sturdy enough to support the weights without breaking. I used a piece of some wooden branch which was lying behind my cupboard (for what purpose it was put there - long forgotten).
Fixing the belt on your body shouldn't be a problem.
Enjoy your training!
P.S.: I used a lighter to burn the cut ends of the belt making them less hairy.