Singer 131 W 104 Four Needle Lock Stich Head Only Industrial Sewing Machine
3/4 needle spacing between outside to outside needle. 1/4 needle spacing between rear two needles. Often used in parachute work. Can be operated with any needle spacing combination between the four needles.
Everything including hooks, feed, needle bar, take up etc all seem to be functioning normal. Sew with one, two, three, or four needles.