An S and S Coupling also known as a Bicycle Torque Coupling or BTC is a coupling

Coupling

A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded.The...

 which enables bicycle

Bicycle

A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....

 frames

Bicycle frame

A bicycle frame is the main component of a bicycle, on to which wheels and other components are fitted. The modern and most common frame design for an upright bicycle is based on the safety bicycle, and consists of two triangles, a main triangle and a paired rear triangle...

 to be separated into smaller pieces, usually to facilitate packing and transporting. They can be built into the frame by the frame manufacturer when the frame is originally assembled or they can be added to a frame after it is finished. A special spanner

Wrench

A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning....

 is available for tightening and loosening the couplers.

Applications

The couplers are usually installed in the top tube and down tube of a single-rider diamond frame. This enables the bicycle to be boxed small enough to avoid the extra fee most airlines charge to check a bicycle as luggage. They can also be installed in tandem

Tandem bicycle

The tandem bicycle or twin is a form of bicycle designed to be ridden by more than one person. The term tandem refers to the seating arrangement , not the number of riders. A bike with two riders side-by-side is called a sociable.-History:Patents related to tandem bicycles date from the late 19th...

 and recumbent

Recumbent bicycle

A recumbent bicycle is a bicycle that places the rider in a laid-back reclining position. Most recumbent riders choose this type of design for ergonomic reasons; the rider's weight is distributed comfortably over a larger area, supported by back and buttocks...

 frames. Santana manufactures a "triplet (or quad) that can be transformed into a tandem by simply removing the center section of the frame."

Characteristics

The couplers are available in stainless steel, cromoly steel, and titanium. The couplers come in different sizes, from 5/8 inch (15.8 mm) to 2 inches (50.8 mm) to match the frame tubing in which they are installed. They are light, about 8 oz. (227 grams) per pair, and as strong as uncoupled tubing. The couplers use a Hirth joint

Hirth joint

A Hirth joint or Hirth coupling is a type of mechanical connection named after its developer Hellmuth Hirth. It is used to connect two pieces of a shaft together and is characterized by teeth that mesh together on the end faces of each half shaft....

 to resist torsion

Torsion (mechanics)

In solid mechanics, torsion is the twisting of an object due to an applied torque. In sections perpendicular to the torque axis, the resultant shear stress in this section is perpendicular to the radius....

.

It takes only a few minutes to separate the couplings.

Alternatives

In order to support the ovalized tube Santana Cycles

Santana Cycles

Santana Cycles is the world's leading manufacturer of tandem bicycles. Santana was founded in 1976 by Bill McCready, an Associate Editor at Bicycling Magazine, and is located in La Verne, California...

 uses between the bottom bracket shells of their tandems, they have developed their own oval couplers.