As various manufacturers started to offer quick detachable couplers, most of them entered the market with their own design, which was different from their competitors. There was very little interchangeability from one brand to another. Efforts to correct this problem began about 50 years ago with the creation of a military specification (MIL-C-4109) for One Way Shut-Off couplers. This design is now the most commonly used and is referred to as the standard industrial interchange. Two Way Shut-Off designs are also being standardized, based on ISO dimensions. However, there are still many different Two Way designs, most of which vary by application. Although there is no organizational standard governing the design of Straight-Thru couplers, a standard industrial design (Foster Series FST) has developed from usage.