A roller chain transfers power from one sprocket to another and is most commonly used on a bicycle. Conveyors, hoists, agricultural machines, oil drilling equipment and small engine vehicles also have them. The steel chain uses cylindrical barrels held in a parallel row with overlapping side supports that enhance tension strength and prevent bending to either side. The rollers fit into the teeth of a sprocket and the chain bends around the sprocket as it rotates. Tension force stretches the chain and can snap a chain link. A few measurements will provide the necessary dimensions for ordering a replacement.
Remove the master link by spinning the sprockets until this chain link is as far from all sprockets as possible. Put the blade of a slotted screwdriver against the open end of the outside retainer clip and push toward the other end of the clip to position the round slots over the pins. Pull the clip off the pins. Pinch the sides of the master chain link with opposing hands and pull outward. The master link should be in one hand and the side plate in the other.
Stretch the roller chain out from end to end and measure the overall length. Place any broken pieces in line before laying a measuring tape beside the length.
Measure the diameter of the rollers by placing a measuring tape under a link with an inch line hash mark on one edge of the roller barrel. The fractional hash mark at the other barrel side shows the roller diameter. Roller diameter is commonly 3/16, or 5/16 of an inch.
Measure the width of rollers by turning the measuring tape perpendicular to the chain. Measure a roller from side plate to side plate of the steel chain. Roller widths may be 3/16, 5/16 or 1/4 of an inch.
Measure the distance between the pins that hold the rollers from centre to centre. This measurement is called pitch and is typically 1/2, or 3/8 of an inch.
Measure the diameter of a pin from the master link. Measure from rounded edge to rounded edge as the roller diameter was measured. Common pin diameters are 5/32, or 1/8 of an inch.
The combination of all measurements except overall length determines the standard type of roller chain. Standard types are No. 35, No. 40, No. 41 and No. 420. Chain suppliers may sell precut lengths by the foot. Order longer lengths and remove the necessary amount of chain link sections to shorten to desired length.