You're thinking of the model 52.
The numbers reference the gun, caliber, action and finish. So...
5 - Series. Full size double stack
9- caliber. 9mm
0 - Standard double action/single action
4- alloy frame black finish.
So anything with a 9 is going to be a 9mm only. 39, 59, 69 are all 9mm. Others like 4006 and 1006 will be 40S&W and 10mm and nothing else. Meaning you can't have a 4006 that's a 9mm.
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