it seems the first M.2 physical socket was implemented in 3020 Micro for WLAN card.  Optiplex Micro model was first introduced in 3020.   Prior to Micro, Dell had Ultra SFF in 7010/9010 and 790/780.  There was no USFF for 3010/390/380.

starting 3020 Dell dropped the DT model line previously used in 3010, 390 and older models.  Starting from 3020 Optiplex form factor is Tower, SFF, or micro.  This has gone on up until the latest 3090 and 3000/5000/7000.

PS Dell added 3090 ultra but does not group it with the three stand alone desktop models probably because the ultra is meant to be used behind a Dell monitor like AIO.

In this discussion I am looking at M.2 wireless card option for Optiplex SFF specifically.  It seems the 3050 SFF board has only one M.2 slot for ssd only.  In 3060 the board has dual M.2 slot one for ssd the other for WLAN.

3050

3060

3040 tower motherboard has no M.2.

3040 micro motherboard has footprints for two M.2 sockets but only one physical socket implementation presumably for M.2 wireless card.

Manual pic 

real pic

Rear panel of 3050 sff has no external antenna connector access.

rear panel of 3060/3070 has external antenna connector access.

note this is for m.2 WLAN card. user can always install PCIe wireless card with antenna or usb dongle.

3050

3060/3070 

The last DT model was the 9010.

"starting 3020 Dell dropped the DT model line previously used in 3010, 390 and older models.  Starting from 3020 Optiplex form factor is Tower, SFF, or micro.  This has gone on up until the latest 3090 and 3000/5000/7000."

So I have to ask - Where did you find that 3090/3000/5000/7000 come in DT models?

Dell Optiplex 3060 uses these types of external antenna:

Dell Y9MPH

or 

Dell 3TJ9N

not sure whether the latter antenna boost has better reception than the former stick style whip antenna.

Dell Optiplex 3060 SFF M.2 WLAN uses this for internal antenna wires:  Dell 9RJ7V TV88M

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