Dingleberries are the circular pieces of foam used to pad the hinge of a flail, primarily to prevent it from being able to wrap wrists, hands, etc. While they are less important safety-wise on bag-head flails than rope-head flails, they are required on both and are usually fairly rigorously checked.
Dingleberries are very easy to assemble. The simplest way is to use pipe insulation of an appropriate diameter, simply cutting off .5-1" high rings and putting them around the chain, then wrapping them once in a length of 1.5" wide cloth tape, holding them closed and covering them. They can also be easily made using short, narrow lengths of blue foam, again covering the rings in cloth tape. While the chain is allowed to be exposed up to 1.5" total, when first adding dingleberries to a flail it's advisable to cover more of the chain than required so that the flail will continue to pass as the dingleberries inevitably compress and the chain potentially stretches.
While the rings can nominally be covered in any form of tape, cloth tape is by far the best for the purpose.
188.8.131.52. The hinged part of the flail must be padded with foam to keep the chain from easily entangling a Weapon or body part. No more than 1 ½ inches of chain may be exposed.