Check the listing for details. Upholstery 13 Gauge, Pocket Spring Unit, Marshall Spring Unit, Innerspring. Condition: New. Listed at 29.95 USD. Upholstery 13 Gauge, Pocket Spring Unit, Marshall Spring Unit, Innerspring Unit. 13 Gauge = Firm 1.8 mm 18" x 18" x 3.5" Design for seat or cushion used. All pocket spring units are compressed for shipping purpose. Please be careful when opening the package. The coils are sew and glue together in the center part, top and bottom still loose, if you need to make the pocket spring more firm, you can attach hog rings to connect the coil on top and bottom. If you need to make a different size, simply open the outside cover and you can cut the coil springs out and use hog ring to hold them together. If you are making different size, you will need to sewing a new outside cover for the pocket spring. 16 Gauge = Soft 1.3 mm 18" x 18" x 3.5" 17 Gauge = Extra Soft 1.1 mm 18" x 18" x 5" Available on our other listings.