I've had this brick for a while, and I've long wondered what it is.
It's a LEGO-compatible 2x4 brick, colored almost exactly the same as the old medium grey. There are no identifying marking, and the only marking of any kind is a single line on the bottom, which I assume is a
The most distinguishing feature is that it has only 1 tube on the bottom, and it doesn't reach all the way down.
I originally found it in a bucket of otherwise genuine LEGO pieces years back, so no clues there.
I'm quite certain it's not a genuine LEGO piece, but it is an odd piece and I've long wondered what it's from?