1.7 x 4.0mm Power Cable Yaesu HTs, FT-817, FT-818

1.7 x 4.0mm coaxial power plug with 6 feet of #24 wire.
This one is commonly used on most Yaesu HTs, as well as the FT-817 and FT-818.

Here's a trick for determining what size plug you have.
You may not have a caliper or micrometer, but you probably have a standard set of drill bits.
5.5mm is very, very close to a 7/32" bit. And a 3/32" drill bit (or audio plug) will slip inside the center barrel of a 2.5mm plug, but not a 2.1mm plug.

Similarly, a 4mm OD connector is very, very close to a 5/32" bit.
And a 3.5mm connector is just a tad smaller than a 1/8" bit.