Re: "Barrel" connectors

On 6/16/2025 2:03 PM, Theo wrote:

Are there any other *mechanical fitting* issues that I may have
overlooked (obviously, there are electrical issues)?

 The trouble with 'just try it' is that the 'trial' sockets can wear over

Yes, but any "test" that looks for mechanical fit suffers from that
same problem.  What you really want is a way to measure without
introducing any other physical object.
Female plugs are relatively easy to sort out -- dial caliper for
the OD and a small selection of drill bits to VISIBLY probe the ID.
But, this only works for two-conductor plugs.

time.  eg if you insist on putting a 6mm OD plug into a 5.5mm OD socket,
it might go but bend the spring contact.  Eventually the 5.5mm OD plugs will
feel loose because the contact is now bent out of place.
 Also you might have a plug that securely fits the OD but it has too large a
hole in the inside so it's a poor fit.  I've previously killed equipment
like that (2.5mm plug on a 2.1mm socket -> poor contact -> voltage drop ->
switching converter has to pull more current to keep up -> fried something).

Exactly.  A fair bit of tension in the (receptacle) spring that secures the
OD of the plug can lead you to thinking it's a good fit -- because it is
next to impossible to move the plug purely laterally under that sort of
tension to see if there is a half millimeter of "play".

I think a series of drill bits to measure the ID is a good plan, then maybe
there's some way to measure the OD while getting 'acceptable' tension on the
spring?

Had manufacturers not wasted so much "label space" on a verbose
"- ---(O--- +" style polarity indicator, they could have included
a single character "code letter" to indicate the dimensions of the
mating plug.
But, manufacturers tend to be ignorant of the needs of their
customers -- too much "bother" to sort out.
[Notice the number of products that don't indicate a manufacturer,
model number, etc.?  "We take great pride in our products -- NOT!"]