Gunter, revenue, engineer and metric chains are different types of chains, commonly used for surveying. Chains are mostly divided into 100 links. While the gunter’s chain is 66 feet long, the revenue chain is 33 feet long and the engineer’s chain is 100 feet long. Metric chains are either 30 meters or 20 meters long.
The different parts of a chain . The part marked 1 is a brass handle which contains a semicircular groove at its end for accommodating arrows during chaining. Parts marked 2 and 3 are the collar and eye bolt. 2 and 3 form a swivel joint with the brass handle. Part 4 is a circular ring which connects the end link marked 5 with the eye bolt. The links are connected with each other with three circular rings marked 6.
All links except the end links are of equal lengths. The link length measures the distance between the centres of the central rings of the joints on either side of the link. The end link forms the complete link length with the brass handle. The end link length measures the distance from the end of the handle to the centre of the central ring of the joint next to the end link. The length, of course, is to be measured while the chain is held straight.
The swivel joint allows rotation of the handle preventing the deformation due to twist in the end link. The three-ring joints provide enough flexibility to prevent the deformation of the links by bending.
For the ease of readability of the chain, different brass tag marks or tally marks are provided in it at definite length intervals, identical tags being placed at identical distances from the either end of the chain. This provides an opportunity to read the length on the chain at any of its points from either of its ends.
All links are made out of SWG No.8–No.12 wires of galvanized mild steel, in accordance with IS:1492-1970, having a diameter of 4 mm usually. The material is sufficiently soft and ductile to withstand hammering when the bent links are to be rectified. It may be noted that a chain with 100 links will have 99 joints between the links and two joints between the handles and the end links. There are 4 × 101 = 404 pairs of wearing surfaces at those joints.
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