Gas grills (outdoor barbecues) used to fasten the
gas cylinders at one edge of the base plate, the
cylinder's base ring fitting into a curved slot. The
new fashion is for gas tanks to be enclosed in
the cupboard under the grill, the base ring fitting
into a circular hole.

To hold the gas tank serely, this requires a
thumbscrew that fits into a hole in the base ring.
Older propane tanks may have solid base rings,
i.e. lack the hole required to secure the tank.
It will save time for purchasers of a new BBQ
to inspect the base ring before attempting to
put an old tank into place . . .
--
Don Phillipson
Carlsbad Springs
(Ottawa, Canada)