Brass Standoffs and Nylon Washers: PCB Mounting FAQ
By Mutual Screw & Supply | Published: 2026-11-04
Category: 제품 리뷰
Straight answers on pairing #4-40 brass hex standoffs with #4 nylon flat washers for PCB mounting: insulation, thickness, torque, and when each part earns its place.
Quick answer
Use #4-40 brass hex standoffs to set board height, and add #4 nylon flat washers only where the fastener head or board edge needs electrical isolation or surface protection. Brass carries current, so a nylon washer under the screw head is the simple way to break that path when your layout requires it.
Why brass and nylon solve different problems
Brass standoffs are conductive, strong, and hold thread well, which makes them a natural choice for spacing and mounting circuit boards and panels. That same conductivity is the reason nylon washers enter the conversation: a nylon flat washer under a screw head or between a board and a metal chassis adds a non-conductive layer without changing the standoff height.
The trade-off is mechanical. Nylon is softer than brass and can creep under sustained clamp load, so a nylon washer is best treated as an insulator and surface protector, not as a structural shim. If your design depends on the washer to carry load or hold torque, metal washers or a different standoff strategy may be the better fit.
Where the #4-40 and #4 sizing actually matters
The #4-40 callout on a brass hex standoff describes a #4 thread at 40 threads per inch, and the matching washer size is a #4 with a .125 in. inside diameter. A #4 nylon washer with a .375 in. outside diameter and .040 in. thickness gives you a defined insulating footprint that clears the screw and spreads load over a wider area than the screw head alone.
Watch the thickness. A .040 in. nylon washer adds a small but real stack height, so confirm clearance above the board before finalizing hardware. If a thinner or thicker washer is needed, that is a specification decision to make from the datasheet rather than by guessing.
PCB mounting questions, answered
- Do I need nylon washers with brass standoffs?
- Only if the design requires isolation. Brass is conductive, so a nylon flat washer under the screw head or between the board and a metal surface breaks the electrical path. If your board is already isolated by layout or a non-conductive enclosure, the washer is optional surface protection rather than a requirement. Decide isolation from the schematic and chassis, not from habit.
- What does a #4 nylon washer's .040 in. thickness change?
- It adds .040 in. to the fastener stack at each mounting point. Check that this extra height does not interfere with connectors, covers, or adjacent components, and account for it when calculating the final board height above the panel. Stack height is cumulative; add washer thickness at every mounting point.
- Can I torque a brass standoff against a nylon washer?
- Nylon is softer than brass and can deform under high clamp load, so treat the washer as an insulator rather than a load-bearing element. Use gentle, consistent tightening and avoid relying on the washer to maintain preload over time. If the joint needs high torque, nylon washers are the wrong interface.
- Will a 1/2 in. brass standoff fit my board spacing?
- The #4-40 x 1/2 in. standoff fixes the gap at 1/2 in. between mounting surfaces. Measure the tallest component on the board and any required clearance before ordering; if 1/2 in. is too short or too long, this specific length is not the right part. Confirm clearance before buying a 100-piece pack.
- How many washers and standoffs should I order?
- Count mounting holes first. The brass standoffs come 100 per package and the nylon washers 1000 per package, so small prototypes may leave significant surplus. Order for the build you have, not for a hypothetical future run. Package quantities favor production runs more than one-off prototypes.
Hardware facts that shape the decision
- 8215-B-0440 | #4-40 X 1/2" Amatom Hex Standoffs | Brass (100 / Pkg.): #4-40 x 1/2 in. hex standoffs made from brass, sold 100 per package. The 1/2 in. length sets a fixed board-to-panel gap, so confirm your clearance before committing to a full pack.
8215-B-0440 | #4-40 X 1/2" Amatom Hex Standoffs | Brass (100 / Pkg.) - #4 x 3/8" OD Flat Washers | .040" Thick | Nylon (1000 / Pkg.): #4 nylon flat washers with .125 in. ID, .375 in. OD, and .040 in. thickness, sold 1000 per package. The defined ID and OD let you plan insulation and load spread around a #4 screw without custom sizing.
#4 x 3/8" OD Flat Washers | .040" Thick | Nylon (1000 / Pkg.)
