I have a case and HDD enclosure that uses that type of key for keeping vandals from stealing my hard drive or turning on the computer. However, it's hard to find a key for that style case from the 1990's. Measure the key lock with a ruler to find the diameter (left to right).

Also, I remember those were used to lock the keyboard from being used, and older systems, such as the IBM PC AT 5170, locked the case to prevent vandals from stealing hardware out of the system.

It's a keyboard lock. When it's enabled, the keyboard will not work. Depending on which BIOS the computer has, it also might prevent the system from booting if the computer is turned on while the keylock is enabled (on my 486 rebuild, the POST process stops at an error that the keyboard is locked, and will not let you continue with the boot process until you unlock it). On most computers, it is nothing more than a switch, easily bypassed by opening up the case and replacing the switch connector with a jumper. There are some computers where it may also physically prevent the case from being opened (or there may be a second separate lock for this purpose), but this was really uncommon on general consumer-grade hardware.

Ah, bummer. So it isn't for Turbo mode after all? The cables from this area are marked as "turbo LED" so I was hoping for that.

If you absolutely wanted to, you COULD connect it to the Turbo header on the motherboard and use it for that. There should be a couple wires coming off the back of the lock leading to a connector, and it should be the same type of connector to fit the Turbo Switch header on the motherboard. 🤣

That's assuming, though, that this is the typical "switch-only" type of lock and not something more proprietary (unlikely, but still a possibility depending on the original intended purpose of the case you are using).

In most cases, the turbo switch uses 3 wires (it depends on if there's an LED that shows the clock speed) or 2. That should work to make the computer go fast or slow. Haven't used the turbo feature in years, but, now it's programs that I made using the MS-DOS Debug program to enable or disable the L1 and L2 cache prospectively.

I will measure the lock and get back to you. 😀 Thanks for all the help.

It's confusing to me that the case would have a turbo LED cable, but no button or obvious way to turn it on. Haha. I am hoping to find a way to access it to slow down the computer to play some of these older games. If I can use this lock as a method to do that, that would be great.

Most likely this case was designed for newer motherboards that use alternative means (Keyboard command, BIOS setting or software) to enable or disable Turbo mode instead of a physical switch. This was more common on Pentium and Socket 7 systems, before Turbo functionality was dropped entirely.