One 12 foot (3.65 metre) 42 links per foot Clock chain with a polished steel finish, specially manufactured, unlike most chain, with a precise pitch for Lantern & Longcase 30hr Clocks.
With most of the original antique chain there was no standardization, each maker, chain manufacturer, or local area had its own particular pitch, which can vary greatly across the range making the selection of a replacement chain difficult. For the chain to run smoothly and efficiently it has to have a consistent pitch, allowing it to engage the sprockets in the movement, if you have problems, it could be
1 The wrong pitch
2 Stretched or worn in sections, or the entire length of the chain.
3 Not a precision pitch chain, (bog chain, as it known by some manufacturers)
4 Worn out sprockets.
Any of these reasons could make the chain to snag and jump on the sprockets, causing the weight to drop a few centimetres, which can usually be heard as a loud bang. One way to ensure that the chain and sprocket will fit and run smoothly is to replace them with a chain and sprocket set ( these are sold in the Longcase movement parts section) as this will remove any question of weather it is the chain, the sprocket, or in some instances both that are the problem.