From the LA Times:
"A bit more surprisingly, McCartney’s instrumental contribution came on a humble cigar-box guitar he played with a slide. The guitar, as it happens, was made here in the Southland by cigar-box guitar aficionado Matty Baratto, whose Cigfiddle creations were featured in a story I wrote last year about a modern-day revival of interest in the homespun cigar-box guitar tradition.
Baratto’s instruments have made their way into other famous hands, including those of Keith Richards and Johnny Depp, and present-day cigar-box players also include ZZ Top’s Billy Gibbons and rocker Steve Miller."