Metallics JMSW20 Washers 6 X 3/8 Mstr Seal Galv (Jar 100)

The JMSW20 is a 6 x 3/8 sealing washer, so it is sized for a #6 fastener with a 3/8 inch outside diameter. If you are running larger screws or need a wider bearing surface against the sheet metal, step up to the next master seal washer size rather than forcing this one.

That is what they are built for. The JMSW20 is a sealing and cushioning washer in galvanized steel, so it both keeps water out of the fastener hole and takes the bearing load against thin material. Galvanized finish gives it corrosion resistance for exterior and damp mechanical work; for heavy salt or coastal exposure, stainless hardware is the better call.

These are loose washers, not screws with washers already bonded on. Metallics positions the master seal washer as a lower-cost substitute for pre-assembled construction fasteners, so you pair the washer with the screw you already stock instead of buying a factory-assembled sealing fastener. You supply the screw.

Same part across all three trades. Metallics lists the application as the electrical, plumbing, heating and air conditioning industries, so a mechanical contractor sealing sheet metal duct penetrations and an electrician mounting an exterior enclosure can standardize on the one washer. It is made in the United States.

Each jar holds 100 washers. The jar packaging keeps them contained on a service truck or in a gang box instead of spilling loose in a drawer, which matters when you are pulling a handful at a time on a punch list.

Order by manufacturer part number JMSW20, Metallics brand, described as Washers 6 X 3/8 Mstr Seal Galv, 100 per jar. That is the only configuration under this number, so there is no finish or size option to specify.

A jar of the JMSW20 washers runs 0.18 lbs, with the container measuring 3 x 3 x 2.15 inches. Light enough that stocking several sizes on a van costs you almost nothing in weight.