Fasteners and Threadlocking

The two thread standards

FRC fasteners are mostly #10-32 and 1/4“-20 (imperial, with thread-per-inch counts).

• #10-32 is the everyday fastener for tube, gussets, and most brackets. A close-fit clearance hole is about 0.196“ (a #9 drill).
• 1/4“-20 is used for higher-load joints. A close-fit clearance hole is about 0.257“ (an F drill); a 17/64“ (0.266“) bit is a common free-fit choice.

Metric (M3, M4, M5) appears on some COTS modules and motors, so keep a metric set on hand too.

Head styles

• Socket head cap screw (SHCS) — cylindrical head, driven with a hex (Allen) key; the strong default.
• Button head cap screw (BHCS) — low, rounded head; good where a low profile or a smooth surface is needed (common on swerve module plates; the Thrifty Swerve bolt kit, for example, ships 10-32 SHCS and BHCS in several lengths).
• Flat head — countersunk flush.

Locking the joint

Vibration loosens fasteners over a season. Counter it with:

• Nylon-insert lock nuts (nylocks) — a nylon ring grips the threads. The most common locking method.
• Threadlocker — anaerobic adhesive on the threads. Loctite 243 (blue) is the standard removable strength; Loctite 263 (red) is high-strength and semi-permanent (needs heat to remove, rarely needed in FRC). Important: standard anaerobic Loctite can craze and crack polycarbonate and other plastics, so near plastic use a plastic-safe option such as Vibra-Tite VC-3 (dried onto the metal fastener first) or Loctite 425.
• Tooth/star lock washers as a mechanical backup.

Practical rules

• Use washers under bolt heads and nuts to spread load and avoid digging into aluminum.
• Don’t over-torque into thin aluminum or you’ll strip the threads ; for tapped holes in thin material, use a nut on the back side instead.
• Standardize on as few fastener sizes as possible so the team only needs a few drivers and a small spares kit.
• Keep a labeled fastener bin and a pit kit with spares of every size you use.

Key takeaways

• FRC standardizes on #10-32 and 1/4“-20 fasteners; close-fit clearance holes are ~0.196“ (#9) and ~0.257“ (F) respectively
• Use socket-head and button-head cap screws, and lock joints with nylock nuts and/or threadlocker
• Standard anaerobic Loctite can crack polycarbonate — use a plastic-safe option like Vibra-Tite VC-3 or Loctite 425 near plastic

This lesson was adapted from learnfrc.com.