Flange isolation · dissimilar metals · bolted thermal breaks

Micarta Washers, Sleeves and Bushings

An insulated joint is only as good as its bolts. If a bolt touches both sides, heat and current go straight through it. Micarta insulating washers and sleeves stop that: the sleeve lines the bolt hole and the washer sits under the nut, so nothing metal bridges the joint.

We machine washers, sleeves and shoulder bushings from STB-1 glass-epoxy laminate to suit your bolt size and grip. It takes 48,000 psi in compression under the nut and has a dielectric strength of 500 VPM.

Where Micarta Washers and Sleeves Go

Flange isolation kits

Washers and sleeves for insulated flanges that separate cathodically protected piping from the rest of the system.

Dissimilar-metal connections

Break the electrical path where aluminum, stainless and carbon steel are bolted together, to prevent galvanic corrosion.

Bolted thermal breaks

Pair washers and sleeves with a thermal break pad so the bolts do not undo the isolation the pad provides.

Electrical equipment supports

Isolate switchgear, bus supports and instrument mounts from structural steel and ground.

Pipe shoes and guides

Insulate the bolts that hold a pipe support block to the rack on hot or cold lines.

Cold and cryogenic joints

The laminate is rated to −270 °C (−454 °F), so the same washers work on refrigeration and cryogenic connections.

Properties That Matter for Washers and Sleeves

Property	Test method	Value
Compressive strength	ASTM D695	48,000 psi (330.9 MPa)
Shear strength	ASTM D732	16,326 psi
Dielectric strength, short time in oil, 1/16″	ASTM D149	500 VPM
Arc resistance	ASTM D495	150 s
Dielectric constant @ 60 Hz	ASTM D150	4.8
Water absorption	ASTM D229	0.35 %
Thermal conductivity	ASTM C518	1.055 BTU·in/hr·ft²·°F
Service temperature	—	−270 °C to 135 °C (−454 °F to 275 °F)

Nominal values tested at room temperature.

See the full specification sheet →

Design Notes for Insulated Bolted Joints

Use a sleeve along the full length of the bolt in the hole, and an insulating washer under each nut or head that bears on the isolated side.
Put a steel washer over each insulating washer to spread the nut load and protect the laminate while tightening.
Check bearing stress under the washer against the 48,000 psi compressive strength, with a suitable safety factor.
Allow for differential thermal expansion between the laminate (2.2 × 10⁻⁵ in/in/°C) and the steel on hot or cold joints.
Test electrical isolation after the joint is tightened.

What to Send for a Quote

Bolt diameter and grip length
Number of bolts per joint and number of joints
Flange size and class, or a drawing of the connection
Whether you need sleeves, washers or one-piece shoulder bushings
Service temperature and whether electrical isolation is required
Required delivery date

Quote Your Micarta Washers and Sleeves

Send your bolt sizes and drawings to sales@bmssi.ca or call 800-580-4195. We machine every washer and sleeve in house.