TECHNICAL GUIDE
Key notch positions, module widths and lengths in this guide follow the PCI-SIG M.2 specification; every KINGCONN socket value comes from the series drawings on this site.
M.2 (formerly NGFF, Next Generation Form Factor) is the card-edge module format that replaced Mini PCIe for SSDs and wireless modules. A module plugs into an M.2 connector — the socket on the motherboard, often called the M.2 slot — at 0.50mm contact pitch. The standard connector has 75 positions; a keyed socket carries 67 contacts because the 8 positions inside the key notch are absent. The M.2 slot only holds the module edge; a standoff and screw at the far end fix the module length.
An M.2 key is a notch cut into the module edge, and a matching rib in the socket. It stops a module from being seated in a slot whose signals it does not support. Notch positions per the specification:
A key — pins 8–15. Wireless modules (Wi-Fi / Bluetooth); usually cut together
with an E key as A+E.
B key — pins 12–19. PCIe ×2, SATA and USB; SATA SSDs and WWAN modules.
E key — pins 24–31. PCIe ×2 and USB; Wi-Fi / Bluetooth modules.
M key — pins 59–66. PCIe ×4 or SATA; NVMe SSDs.
B+M key — a module with both notches fits a B-key or an M-key socket, and runs at the
narrower PCIe ×2 link.
The socket is keyed for one position only. An M-key socket accepts M-key and B+M-key modules; an E-key socket accepts E-key and A+E-key modules. This is the first thing to fix in a design, before pitch or height.
An M.2 size code is width × length in millimetres. Widths defined by the specification are 12, 16, 22 and 30mm; lengths are 16, 26, 30, 38, 42, 60, 80 and 110mm. So 2280 is a 22mm-wide, 80mm-long module, 2230 is 22 × 30mm, and 22110 is 22 × 110mm. The M.2 connector is the same for all of them; the board's standoff position sets which lengths fit.
Stack height is the gap between the motherboard and the underside of the module when mated. It has to clear the components under the module — double-sided SSDs need more room than single-sided wireless cards. The KINGCONN M.2 series lists 0.50mm-pitch, 67-contact sockets in 3.2mm, 4.0mm and 4.2mm stack heights, rated for 60 insertion cycles — a module socket is installed once and serviced rarely, and the rating reflects that.
Before M.2, wireless and storage modules used Mini PCIe: a 52-pin card edge on a 30 × 50.95mm full-size card. Industrial PCs and gateways designed around it keep shipping for years, so KINGCONN keeps Mini PCI sockets in 6.7mm and 6.8mm heights on the catalogue. The two formats are not interchangeable: different pin count, different key, different footprint.
Decide the key (from the module), the length (from the standoff position) and the stack height (from component clearance), then open the M.2 series page for drawings, or email service@kingconn.com.tw with the module type and quantity. Related: the M.2 & Mini PCI socket selection guide and the expansion card slots overview.