http://magpul.com/Admin/Public/DWSDownload.aspx?File=%2fFiles%2fFiles%2fPDF%2fPropaganda%2fM-LOK_2015_FAQs.pdf Magpul Industries - M-LOK DESCRIPTION AND FAQ DOCUMENT] The slots provide metric 20 mm length intervals, and accessories can be mounted either within a slot or bridging between slots, making it possible to adjust the position of accessories in smaller intervals than the length of the slot.