A Slocket is a simple adapter board that allows Slot 1 motherboards to utilize PPGA or FC-PGA processors. They resemble the PCB on a Slot 1 processor, complete with open PPGA/FC-PGA processor socket and a selection of hardware jumpers. Standard, non-name Slockets might not have any special features to speak of, but higher priced, name brand models usually include several options intended to facilitate overclocking.
The most important feature you should look for in a Slocket adapter is the ability to adjust the core voltage. This feature consists of a set of hardware jumpers that can either increase or decrease the detected core voltage of the CPU. This effectively emulates the Slot 1 processor voltage and sends a different core voltage signal to the motherboard, depending on the setting chosen. This can be useful for motherboards that do not have voltage control in the software BIOS, or for those who require a higher voltage on a motherboard with CPU auto-detect.
If you're planning on using the Slocket adapter with a one of the newer, .18 micron Celerons, then it needs to be Coppermine-ready. Most retailers only stock the newer models of Slockets, but it never hurts to make sure by reading the package and looking for a reference to FC-PGA CPUs. One area of concern is the available real-estate for specialized CPU coolers. With many Slockets, this can be a real issue, and capacitors or even the CPU retention mechanism can really get in the way of larger heatsinks.
So which CPU Slocket should you use? The first rule of thumb is to match brands if possible. If your motherboard manufacturer produces a Slocket adapter, then you'll be best off to purchase that one, if at all possible. Combining like brands of motherboards and Slockets can yield greater stability, but the most important factor is product support. If you have a technical problem with your system configuration, the technicians will have a much easier job diagnosing your problem if you are using both a motherboard and Slocket from their company. If this isn't an option, you can't go wrong with the Abit Slocket III, MSI 6905Master or Iwill Slocket II.