I went thru the lyrics to chain gang song like 1000 times.
And the clue is "CHAIN"
what sort of CHAIN?
A chain is a unit of length?
Specific uses for chain include:
* Bicycle chain, chain that transfers power from the pedals to the drive-wheel of a bicycle thus propelling it
* Chain drive, the main feature that differentiated the safety bicycle
* Chain gun, type of machine gun that utilizes a chain, driven by an external power source, to actuate the mechanism rather than using recoil
* Chain pumps, type of water pump where an endless chain has positioned on it circular discs
* Chain-linked Lewis, lifting device made from two curved steel legs
* Chainsaw, portable mechanical, motorized saw
* Curb chain, used on curb bits when riding a horse
* Door chain, a type of security chain on a door that makes it possible to open a door from the inside while still making it difficult for someone outside to force his or her way inside
* Keychain, a small chain that connects a small item to a keyring
* Lead shank (or "Stud chain"), used on difficult horses that are misbehaving
* O-ring chain, a specialized type of roller chain
* Roller chain, the type of chain most commonly used for transmission of mechanical power on bicycles, motorcycles, and in industrial and agricultural machinery
* Snow chains, used to improve traction in snow
* Timing chain, used to transfer rotational position from the crankshaft to the valve and ignition system on an internal combustion engine, typically with a 2:1 speed reduction.
* Ball and chain, phrase that can refer to either the actual restraint device that was used to slow down prisoners, or a derogatory description of a person's significant other
* Bicycle lock (or "bicycle chain"), lockable chain
* Leg iron chains (Fetters), an alternative to handcuffs
* Chain link fencing, type of fencing that utilizes vertical wires that are bent in a zig zag fashion and linked to each other
* Chain of office, collar or heavy gold chain worn as insignia of office or a mark of fealty in medieval Europe and the United Kingdom
* Chain weapon, a medieval weapon made of one or more weights attached to a handle with a chain
* Nunchaku, karate sticks linked by a chain
* Omega chain, a pseudo-chain where the 'links' are mounted on a backing rather than being interlinked
* Pull switch, an electrical switch operated by a chain
* Flat chain, form of chain used chiefly in agricultural machinery
* Decorating clothing, some people wear wallets with chains connected to their belts, or pants decorated with chains
* Jewelry, many necklaces and bracelets are made out of small chains of gold and silver
* Jack chain, a toothed chain used to move logs
* Ladder chain, a light wire chain used with sprockets for low torque power transmission
* Chains can also be used as a percussion instrument for special effects, such as in Schönberg's Gurre-Lieder and Janáček's From the House of the Dead