Engineering and Component Solution Forum – TechForum │ Digi-Key

One common question that is asked of Techs at Digi-Key is to trying to verify the correct substitute wall mount AC to DC world power supply. The unmanageable specification to find on many of these office supplies is what size if the inner diameter of the plug / connection. This is made more unmanageable by the fact that the two most common size of plugs at 2.1 millimeter ID x 5.5 millimeter OD and 2.5 millimeter ID x 5.5 millimeter OD. Since this measurement is besides close to use a rule and fitting a caliper ( if available ) inside a 2.1 or 2.5 millimeter hole is very difficult to do accurately. This leaves you with two options. You can buy one and get an Adapter ( 2.1 to 2.5, or 2.5 to 2.1 ) in case you buy the incorrect one, or there are a pair tricks that can help identify which size you have. Please make sure the office supply is de-energize before trying any of these methods .
The Toothpick
Most round toothpicks are manufactured to be between 2.1 and 2.2 millimeter in diameter. If you slide this into the end of a 2.1 millimeter ID plug it will be close and would not fall out when tipped up. When placed in a 2.5 millimeter ID plug the toothpick is loose and will fall out when tip.
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The Pen
If you take a pen the widest target on the gratuity is going to be a standard 2.25 mm – 2.35mm. This means that the entire point will not go into a 2.1 millimeter plug, however will go into a 2.5 millimeter hack.

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Test Lead
This is the a small snatch more of a flim-flam. Most test moderate you will find have a diameter of 2 mm and paroxysm in both the 2.1 and 2.5 millimeter plugs sol you have to look at the opening. Being very close to the same on the 2.1 you will notice little to gap between the test conduct and the barrel plug. When placing the examination lead in the 2.5 millimeter plug you will see a noticeable gap around the spark advance .
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The Drill Bit
If you ’ re like me there are always drill bits handy. By converting the drill act size from inches, we can use the bits to perform a simple trial, similar to the toothpick method acting.
A 5/64in. ( 1.98mm ) morsel will slide into a 2.1mm connection but a 3/32in. ( 2.38mm ) bit will not.
A 3/32in. ( 2.38mm ) bit will slide into a 2.5mm connection but a 7/64in. ( 2.78mm ) bit will not .

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