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.
What is M.2?
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.
M.2 key types: A key, B key, E key and M key
| Key | Notch (pins) | Interfaces on the edge | Typical modules |
|---|---|---|---|
| A key | 8–15 | PCIe ×2, USB 2.0, I2C, DisplayPort ×4 | Wi-Fi / Bluetooth modules (usually cut as A+E) |
| B key | 12–19 | PCIe ×2, SATA, USB 2.0 / 3.0 | SATA SSDs, WWAN / LTE modules |
| E key | 24–31 | PCIe ×2, USB 2.0, I2C, CNVi | Wi-Fi / Bluetooth modules (2230) |
| M key | 59–66 | PCIe ×4, SATA | NVMe SSDs (mostly 2280) |
| B+M key | 12–19 and 59–66 | PCIe ×2, SATA | fits either socket, runs at ×2 |
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. The socket is keyed for 1 position: an M-key socket accepts M-key and B+M-key modules; an E-key socket accepts E-key and A+E-key modules. A B+M module seated in an M-key socket runs at PCIe ×2, not ×4. This is the item to fix in a design before pitch or height.
How to read the key off a module
Hold the module with the edge contacts down and the notch toward you: a notch near pins 8–15 is A key, a little further in at pins 12–19 is B key, mid-edge at pins 24–31 is E key, and near the far end at pins 59–66 is M key. A module with 2 notches is B+M (or A+E). SSD labels usually print "M key" or "B+M key"; Wi-Fi modules print "A+E key" or "E key". If the notch is hard to read, count contacts: on an M-key module the short side beyond the notch has only 5 positions left (pins 67–75 minus the notch), which is the quickest tell.
Common mismatches, and what the socket can and cannot stop
The 3 that recur: a B+M-key SATA SSD seated in an M-key socket wired for PCIe only — it fits, but the board routes no SATA to that socket and the drive never appears; a 2280 SSD bought for a board that only has a 2242 standoff hole; and an industrial board that keeps a Mini PCIe wireless card but is specified with an M.2 E-key socket — pin count, key and footprint all differ, and no socket swap fixes it. The socket only rejects the wrong key. Whether the interface is routed and whether the length has a standoff are board decisions, and they belong in the specification.
M.2 sizes: 2230, 2242, 2260, 2280, 22110
| Size code | W × L (mm) | Where you meet it |
|---|---|---|
| 2230 | 22 × 30 | Wi-Fi / Bluetooth (E key), small SSDs |
| 2242 | 22 × 42 | WWAN, industrial SSDs |
| 2260 | 22 × 60 | uncommon, some industrial |
| 2280 | 22 × 80 | mainstream NVMe / SATA SSDs |
| 22110 | 22 × 110 | server and enterprise SSDs |
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 and 22110 is 22 × 110mm. A board that has to accept several lengths carries several standoff holes and a floating standoff, which is a mechanical decision, not a connector decision.
Stack height: the value that picks the socket
| KINGCONN M.2 series | Published value |
|---|---|
| Contact pitch | 0.50 mm |
| Contacts | 67 (75 positions less the 8 inside the notch) |
| Stack height | 3.2 mm, 4.0 mm, 4.2 mm |
| Durability | 60 cycles |
| Housing / contacts | LCP UL94V-0 / phosphor bronze |
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, and a heat spreader on the SSD adds to the height above. 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. Pick the key from the module, the length from the standoff position and the stack height from component clearance, in that order.
Mini PCIe and M.2
Before M.2, wireless and storage modules used Mini PCIe: a 52-pin card edge on a 30 × 50.95mm full-size card (the short card is 30 × 26.8mm). 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 2 formats are not interchangeable: different pin count, different key, different footprint. mSATA uses the Mini PCIe connector with SATA signals, which is why sockets labelled for the 2 formats exist.
M.2, Mini PCIe and mSATA compared
| Format | Edge contacts | Pitch | Module size (mm) | Interfaces |
|---|---|---|---|---|
| M.2 | 75 positions (67 contacts when keyed) | 0.50 mm | 22 × 30 / 42 / 60 / 80 / 110 | PCIe ×4, SATA, USB, wireless |
| Mini PCIe | 52 pins | 0.8 mm | 30 × 50.95 (short card 30 × 26.8) | PCIe ×1, USB 2.0 |
| mSATA | 52 pins (same connector as Mini PCIe) | 0.8 mm | 30 × 50.95 | SATA |
All 3 formats are mechanically "a card-edge socket plus a standoff at the far end", and none of the sockets accept another format's module. Mini PCIe and mSATA share a connector and leave it to the board to route PCIe/USB or SATA; M.2 builds the interface difference into the key. That is why industrial boards keep a Mini PCIe socket next to an M.2 socket: the supply life of the older modules outlasts the adoption curve of the new format.
KINGCONN M.2 and Mini PCI sockets
7NGFF-F0-0302NGFF 67PIN M KEY H:3.2mm
7NGFF-F0-0305NGFF 67PIN B KEY H:3.2mm
7NGFF-F0-0402NGFF M KEY H:4.0mm
7NGFF-F0-0428NGFF M KEY H:4.2mm GEN4
7MPCI-F0-0670MINI PCI EXPRESS H:6.7mm
7MPCI-F0-0680MINI PCI EXPRESS H:6.8mmM-key and B-key M.2 sockets at 3.2, 4.0 and 4.2mm stack heights, and Mini PCI Express sockets at 6.7 and 6.8mm.
Shortlist and RFQ
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.