To expand on what Loco said I'll offer the following, which I posted recently on another forum to answer a similar question.
The earliest versions (first few years of production) had metal followers and a hole in the base plate. They had a two piece body with the back portion staked on. Mags held 10 rounds. These are sought after by collectors and are hard to find.
Next version had a one piece body with metal follower and a hole in the base plate. Mags held 10 rounds. These were made from the 1960s thru I believe the mid 1980s. These are generally preferred over the newer versions because folks like the metal followers better.
Special mags where made for the Model 41-1 to handle .22 shorts and only held 5 rounds. They were basically factory modified versions of the regular magazine, but had a special follower, plug, different spring and spring guide. See pics below. These are rare and pricey today.
The newest version of the Model 41 mags have plastic followers (black and orange) and come in 10 round and 12 round configuration. They do not have holes in the base plate. These are currently available through many online sources.
I don't have any newer mags but I do have some older ones with the metal followers:
Here are some disassembled examples. Metal follower mag on top and a rare Model 41-1 .22 short mag on the bottom. You can see the differences in the components.
Here is a shot of the top of the mags so you can see the metal followers. Regular mag on right, .22 short mag in middle and .22 short mag body only on the left. You can see the shorter follower, plug and "U" shaped piece at the front.....all required to make the .22 short cartridge feed properly.
Model 41-1 .22 short mags only go to 5.
Holes on the bottom of the base plate make disassembly easier. These are Model 41-1 .22 short mags.......you can tell because the spring guide is stainless steel vs the blued steel spring guides on the regular mags. All Model 41 mags I've seen have the lazy ampersand (&) on the bottom so you can't use that to date them like you can with the Model 41 barrels.