Which Mills model is this machine?

[LMMIII]

Hello all - I recently became the owner of my first slot machine. Been a collector of video games and pinball machines for years.

I know this is a newer model of a Mills machine, but does anyone know the official model name? I've seen it referred to as "21 Bell", "Mills Bell-o-Matic." And descriptions online refer to the unit as a "Mills compact", "high-top", "open front"...

I looked at the serial number online and it didn't confirm the model for me. There was also a stamp of 1964 near the serial number - I imagine this is the production run date.

Any thoughts? Thanks for the help.

Here are the pics:

[JHSS-1944]

LMMIII ; Welcome to the forum.
nice looking machine, a bit newer than I'm use to collecting. I have hard these referred to both open front & compacts. not sure which is correct.
if it's complete ,congratulations !!!! , parts can be hard to come by OR be a bit pricey when found.
hang tight , no doubt a fellow collector will have better information.
jeff H.

[nvmos2]

Front Open is a nickname that could be applied to several different models made by different manufacturers.

"By 1962 Mills was no longer the industry's pacesetter, but they were determined to regain that distinction. They tried to accomplish this with the introduction of an illuminated all-steel front-opening machine dubbed the Mills COMPACT.
Its small case utilized the old mechanism resting on a pull-out baseplate on a rotating turnstile, allowing it to be pivoted for repair without removing it from the cabinet. These attractive new machines, costing between $600 and $700,
sold well throughout Nevada." .........Marshall Fey

You have a Mills Compact, which is a Front Open (or Open Front) machine.
It is NOT a High Top or 21 Bell;
a High Top refers generally to several different Mills models with a specific cabinet design;
a 21 Bell is a specific High Top model with a special award payout for 777 on the reels.

Here is an example of a Mills High Top 21 Bell: