Coaxial Power Connector - Common Sizes and Interchangeability

Common Sizes and Interchangeability

The most common plugs are 5.5 mm in outside diameter (OD) and 9.5 mm in length. Two inside diameters (ID) are common in the plugs for this size, 2.1 mm and 2.5 mm, and ideally the pin in the jack should match. Generic plugs are often named after the inside diameter, so these types will be seen described as 2.1 mm DC plugs and 2.5 mm DC plugs respectively. These two sizes are easy to visually confuse, unless compared side by side. Slightly smaller 5.0 mm OD plugs are sometimes used in both 2.1 mm and 2.5 mm sizes, and are also frequently misidentified. Plug connector barrels for all of these sizes are typically 8 mm to 14 mm in length, with 9.5 mm most common.

After the two common 5.5 mm OD plugs, the next most common size is 3.5 mm OD with a 1.3 mm ID, commonly 9.5 mm in length but both longer and shorter versions also exist. These 3.5 mm OD plugs are normally used for lower voltages and currents.

There are also 6.5 mm OD plugs with a 3 mm ID, 3.8 mm OD plugs with either a 1.35 mm or a 1.05 mm ID, 3.5 mm plugs with a 1.3 mm ID, and many less common sizes.

Use of a plug designed for a larger pin, for example a 2.5 mm plug with a 2.1 mm pin jack, may work adequately depending on the design of the jack, but often the result is an unreliable contact or occasionally no contact at all. A pin that is too large for the plug will not allow insertion of the plug at all. Similarly, a larger plug barrel (OD) may not fit at all; a smaller one may fit but may not make a reliable contact. Length is less critical than the diameters but is sometimes a consideration; in general a longer plug is no great problem but a shorter one may fail to contact the pin reliably or at all.

It is possible to obtain connector size adapters with a DC coaxial female connector on one end, and a different-sized DC coaxial male connector on the other end.