Which coupler type is similar to the D coupler but has a longer stem?

The choice that is correct is the S coupler, which is similar to the D coupler but features a longer stem. The S coupler, commonly used for serving stouts and porters, was designed to accommodate the specific needs of beers that benefit from a different gas pressure. The longer stem of the S coupler provides better clearance when connecting to kegs, especially in situations where space is a constraint or when keg positioning might impact the ability to connect properly.

The D coupler is often used for many American beers and has a shorter stem, making it suitable for standard kegs. The A coupler is used predominantly for European ales, while the M coupler is less common and typically used for specific types of imports, particularly European kegged beers. Each type of coupler has its distinct design intended for different keg threading systems, which is important to ensure optimal dispensing and maintain beer quality.