A bit converter, also known as a pelham rounding, is used on pelham bit

Pelham bit

A pelham bit is a type of bit used when riding a horse. It has elements of both a curb bit and a snaffle bit. In this respect a pelham bit functions similar to a double bridle, and like a double bridle it normally has "double" reins: a set of curb reins and a set of snaffle reins. Because it has...

s to change them from two-rein bits to one-rein bits. It is a leather strap that attaches from the snaffle ring to the curb ring, onto which the rein is then attached to the loop made between the two rings. A bit converter is very helpful when riding the cross-country phase of eventing

Eventing

Eventing is an equestrian event comprising dressage, cross-country, and show jumping. This event has its roots in a comprehensive cavalry test requiring mastery of several types of riding...

, so that a rider using a pelham does not have to keep track of two reins— especially helpful when riding drop fences, which require the rider to slip the reins and then gather them back up on landing. It is also commonly seen used by children, who may have not yet become skilled enough to handle two reins with ease. However, the bit converter diminishes the rider's ability to apply the curb and snaffle functions of the pelham independently and discriminately, and thus is usually considered unsuitable for other types of riding; it is illegal in hunt seat

Hunt seat

Hunt seat is terminology used in the United States and Canada to refer to a style of forward seat riding commonly found at American horse shows. Along with Dressage, it is one of the two classic forms of English riding. The Hunt seat is based on the tradition of fox hunting...

equitation, for example.

A bit converter is also frequently known as 'roundings' or 'pelham roundings'.