Your description is correct, as far as the older models that I've seen.
Newer models that also read DC current use a hall effect device for sensing
the DC current, from what I've read about them.

If the jaws are laminated steel, they're probably just about indestructable,
but if they're formed ferrite material, there may be a break in a "jaw"
section, interrupting the induction path.
The break might not be a physical fracture from abuse, instead, it could be
some foreign material interrupting the magnetic circuit. The parts of a
ferrite inductive pickup should meet squarely, with no gaps.

The hex nut locations you described in your follow-up post sound like the
associated screw heads may be in recesses on the opposite side, and that the
screw heads may have been concealed by some sort of filler that
conceals/obscures their location, and also lets the manufacturer know that
the case has been opened (voiding any warranty obligations).

In old equipment I've seen asphalt-type filler used to conceal fasteners,
and newer equipment a silicone or a hot glue-type filler has been used.

--
Cheers,
WB
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wrote in message
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I picked up this probe at a yard sale for 5.00. After cleaning up the
connectors and installing a new AAA battery it works on resistance and
voltage ranges with the accessory cables supplied but when clamped
around a current carrying conductor it reads zero. I'm guessing that
there must be some kind of coil wrapped around the jaws internally on
this thing in some way. Current flowing through a conductor would
induce a voltage into this "primary" with a "secondary" connected to
the meter. I'm guessing here. I'm not really sure what is inside of
this meter. Can anyone tell me something about the theory of this type
of instrument and if they have any experience with this model. I may
have to get inside and would really appreciate some help with that as
well. There doesn't seem to be an easy way to do that without a
special tool. The company was no help at all.Thanks, Lenny.