A Master Key System is a system that allows different levels of keying for different levels of access. Simply put, some keys will access more areas than others. You can have a simple Master System or it can get very complex, depending on your needs. The sample page is for a 7 pin system, but master keying is the same for a 6 pin until you get to page 64 of the system. There are 64 pages like this in a 6 pin system, and 256 in a 7 pin system.
I am going to go over the levels of Master keys starting with just one page of a sample system. The 7 digit numbers are the key bittings, or key codes, and the designations next to them tell us what they are. Any designation that starts "CK" is a "Change Key" (an individual key) which means that key only opens locks keyed to that code. It may only be one door, but it could be many. For example: CK1 could be the exterior door key, but if you have 3 exterior doors keyed to CK1 it would open them all. That would not be master keying, but would just be keying alike. There are 64 "CK" keys per page.
Any key designation that starts with something other than "CK" is a type of Master Key. Each designation that starts with"BM" is a "Block Master" which means it opens anything in that block (which would be the 4 "CK" keys below it). For example: If CK1 is the exterior office, and CK2 is the exterior warehouse, the BM1 would open them both. We are now talking about Master Keying. There are 16 "BM" keys per page.
The next level up is the "VGM", or "Vertical Group Master". It opens anything in that vertical group. For example: VGM1 would open anything keyed to the 16 Change Keys under it, from CK1 to CK16. There are 4 "VGM" keys per page. The next level up is the "PM" or "Page Master" which will open anything on that page.
On the upper left corner of the page you will see more levels of Master Keys. "GPM" is the "Grand Page Master" which will open 4 pages of the system. Above that is the "GGPM" or "Great Grand Page Master", which will open 16 pages of the system. The next level up is "GGGPM" or "Great Great Grand Page Master", but is only available on a 7 pin system. It would open 64 pages of the system, and there are 4 available on a 7 pin system. On any system there is always a Grand Master available that would open anything. You can use as many or few of the different levels of Master Keys as you need.
As you can see SFIC Systems can be massive. There are some other Master Keys that I skipped over - "RM" or "Row Master" and "HGM" or "Horizontal Group Master", but you can probably figure them out from their description. Please feel free to call or email if you have any specific keying needs. We also have some "Request For Quote" forms available, which I have included links to.