On Monday, May 1, 2017 at 9:35:25 AM UTC-7, N_Cook wrote:
On 01/05/2017 13:44, wrote:
First, you are writing of some sort of casual static discharge where the thumbdrive is in the current path.... Purchase a very cheap thumbdrive, and try to wreck it via static. You should be reassured by the results.

I assume an old SD card would make a reasonable stand-in. I'll dig out
an old ion-generator and have a go.

An SD card is NOT a reasonable standin.
The USB connector shell is a Faraday shield, which SD lacks.
The finger contacts for power and GND of a USB connector are the longest
(most likely to engage first), but all SD pins are similarly accessible.
USB data goes through a differential transceiver, but an SD card sends
and receives single-ended logic signals.
A 'dead' SD card may be hard to
detect, unless your reader can exercise all its modes of data transfer.

As far as electrical properties of the connector are concerned, only the
power and ground pins have similar properties between SD and USB (and those
are NOT the static-sensitive pins).