Shimano manufactures many components for bicycles. Besides pedals, brakes and shoes it also supplies chains. The chain you choose for your bike depends on what type of bike and how many gears you have. Two chains from Shimano are the HG50 and HG70.
Both the Shimano HG50 and HG70 have 114 links held together with nickel-plated link pins. The outer links (chains are made up of alternating inner and outer links) bulge out to prevent crimping and have a bevelled edge to increase flexibility.
The HG50 chain is all black and weighs 327 grams. The HG70 alternates black inner links with grey outer links. The HG70 weighs 310 grams. The HG50 is typically priced lower than the HG70.
The HG50 chain is recommended as a replacement chain for the STX and Alivio groupsets (a groupset is the gears, derailleurs, shifters and brake levers of the bike). The HG70 is recommended for the 105 Shimano Road Group and the Deore Shimano group for mountain bikes.