Why Use Micro Washers?
Micro washers serve the same purpose as standard flat washers but are sized for micro fastener assemblies where a #6 or larger washer would not fit. They distribute the clamping load from a screw head or nut across a larger bearing area, protect soft or finished surfaces from damage during tightening, prevent a small screw head from pulling through thin or soft materials, and provide a smooth bearing surface that reduces friction during assembly.
This category includes micro flat washers in imperial sizes for #0 through #4 screws and metric sizes for M1 through M3 screws, available in stainless steel, brass, and nylon.
Common Uses for Micro Washers
Micro washers are commonly used in electronics enclosure assembly, circuit board and panel mounting, optical instrument housings, camera bodies, eyeglass frames, medical device construction, robotics and drone frames, precision instrument panels, and small mechanical assemblies where a standard washer is too large for the screw size being used.
They are also used under micro nuts to protect the mating surface from nut rotation during tightening, and in assemblies involving soft or easily scratched materials such as plastic housings, anodized aluminum panels, and acrylic where a bare screw head or nut could cause cosmetic or structural damage.
Imperial Micro Washer Sizes
Imperial micro washers are sized by screw number to match standard Unified National micro screws. The washer inner diameter is sized to clear the screw shank, and the outer diameter and thickness vary by washer standard and product. Available imperial micro washer sizes include:
- #0 (fits #0-80 screws)
- #1 (fits #1-64 and #1-72 screws)
- #2 (fits #2-56 and #2-64 screws)
- #3 (fits #3-48 and #3-56 screws)
- #4 (fits #4-40 and #4-48 screws)
The washer number corresponds to the screw number it is designed to fit. A #2 micro washer fits a #2-56 or #2-64 screw regardless of thread pitch, as the thread pitch does not affect the screw shank diameter.
Metric Micro Washer Sizes
Metric micro washers are sized by nominal screw diameter in millimeters to match ISO metric micro screws. Available metric micro washer sizes include:
- M1 (fits M1 x 0.25 screws)
- M1.2 (fits M1.2 x 0.25 screws)
- M1.4 (fits M1.4 x 0.3 screws)
- M1.6 (fits M1.6 x 0.35 screws)
- M2 (fits M2 x 0.4 screws)
- M2.5 (fits M2.5 x 0.45 screws)
- M3 (fits M3 x 0.5 screws)
Metric micro washers are standard in European and Asian-manufactured products and are sized to fit metric micro screws by nominal diameter. Always match the washer to the screw diameter, not the thread pitch.
Micro Washer Materials
Micro washers are available in 18-8 stainless steel, 316 stainless steel, brass, and nylon. Select the material based on the corrosion environment, the mating fastener material, the conductivity requirements of the assembly, and the appearance of the finished product.
18-8 stainless steel micro washers provide good corrosion resistance for most general-purpose applications and are the most common choice for micro fastener assemblies. 316 stainless provides better resistance to salt and chloride exposure for marine, coastal, and medical applications. Brass micro washers are electrically conductive and non-magnetic, commonly used with brass micro fasteners in electrical and optical assemblies. Nylon micro washers are non-conductive and soft enough to protect delicate surfaces from scratching or marring, often used in electronics and plastic housing assemblies where metal washers could cause surface damage or create electrical contact.
Stainless Steel Micro Washers
Stainless steel micro washers in 18-8 and 316 grades are the most widely used micro washers for general precision assembly. They provide a hard, corrosion-resistant bearing surface under the screw head or nut, distribute clamping load without deforming, and are compatible with stainless steel micro screws and nuts for a consistent material assembly.
18-8 stainless steel is suitable for most indoor and moderate outdoor environments. 316 stainless steel is preferred for marine, coastal, and high-humidity environments where better chloride resistance is needed.
Brass Micro Washers
Brass micro washers are electrically conductive, non-magnetic, and naturally corrosion resistant in many environments. They are commonly used in electrical enclosure assembly, optical instruments, RF hardware, and any application where a conductive, non-ferrous washer is specified or where the assembly uses brass micro screws and nuts throughout.
Brass is softer than stainless steel. In applications with repeated disassembly or high clamping loads, brass micro washers may deform at the bearing surface over time. For frequent reassembly applications, consider stainless steel micro washers.
Nylon Micro Washers
Nylon micro washers are non-conductive, lightweight, and soft enough to protect delicate surfaces from scratching during assembly. They are commonly used in plastic housing assembly, circuit board mounting, and any application where the washer must electrically isolate the fastener from the mating surface or where a metal washer could mar the finished surface.
Nylon micro washers are not suitable for high-temperature applications, as nylon softens at elevated temperatures and can lose its shape under sustained load. They are also less dimensionally stable than metal washers and should not be used in applications where precise washer thickness is critical to the joint design.
Micro Washers vs Standard Flat Washers
Standard flat washers begin at approximately #6 screw size and go up through larger diameters. Micro washers cover #0 through #4 in imperial and M1 through M3 in metric, filling the size range below what standard flat washers cover.
If you are working with a #4-40 screw, both a micro #4 washer and some standard #4 washers may be available depending on the specific outer diameter and thickness needed. Check the washer dimensions against your assembly requirements before selecting, as washer standards for small sizes can vary between manufacturers.
When to Use a Micro Washer
Use a micro washer when the screw head or nut bears directly on a soft, thin, or finished surface that could be damaged by the clamping force. Use a micro washer when the clearance hole in the mating material is close to the screw head diameter, creating a risk that the head could pull through under load. Use a micro washer to reduce friction under the nut during tightening, which allows more of the applied torque to be converted into clamping force rather than lost to friction.
In very compact assemblies, there may not be space for a washer at all. In those cases, select a micro screw with a larger head bearing surface such as a pan head or truss head, which provides more bearing area without requiring a separate washer.
Related Categories
Micro Washers FAQs
What size micro washer do I need for a #2-56 screw?
Use a #2 micro washer for any #2 screw, including #2-56 and #2-64. The washer size is determined by the screw number, which corresponds to the shank diameter. Thread pitch does not affect which washer size to use.
What size micro washer do I need for an M2 screw?
Use an M2 micro washer for any M2 x 0.4 screw. Metric micro washers are sized by nominal screw diameter in millimeters and are compatible regardless of thread pitch within the same diameter designation.
Can I use a nylon micro washer with a metal micro screw?
Yes. Nylon micro washers are commonly used with stainless steel or brass micro screws when electrical isolation or surface protection is needed. There is no galvanic concern when pairing nylon with metal since nylon is not a conductor and does not participate in galvanic reactions.
What is the difference between a #4 micro washer and a standard #4 flat washer?
Both are designed to fit a #4 screw, but a micro washer typically has a smaller outer diameter and thinner profile suited to compact precision assemblies. Standard flat washers may be available in a wider range of outer diameters and thicknesses. Check the washer dimensions against your assembly requirements before selecting.
Do metric and imperial micro washers interchange?
No. Metric and imperial micro washers have different inner diameters and should not be substituted for each other. An M2 washer and a #2 washer are close in size but are not interchangeable. Always match the washer to the correct thread standard and screw diameter.
Do you sell micro washers in bulk?
Yes. Micro washers are available in bulk quantities with competitive pricing at volume. Contact us for pricing on large or recurring micro washer orders.