R23a — commercial fastener allowance (verbatim summary)

From the V5RC Robot Inspection KB:

What this means in practice for our kit:

• VEX uses 8-32 throughout. So our team focuses on #8 commercial hardware to match.
• Standoffs and spacers up to 2.5″ long are legal as long as they fit a #8 screw. Our 7/8″ spacer is well within this.
• Nuts and washers are broadly allowed. Thread-forming locknuts, Belleville washers, etc. all fit under "any commercially available nut/washer."
• Shoulder bolts have a strict size limit. Shoulder ≤ 0.20″ long, ≤ 0.176″ diameter. Most commercial shoulder bolts exceed both — verify carefully.

What's legal (verified) vs what's not

How to verify a part before buying

1. Check R23a. If it's a screw, nut, washer, standoff, or non-threaded spacer that fits standard sizes, it's probably legal.
2. Check the V5RC Legal Parts List. Referenced by R17/R20. This is the authoritative allow-list for non-fastener parts.
3. Check the Override Q&A. Search for the specific part type. If someone has asked, the answer is binding.
4. Submit a new Q&A. If the part isn't covered, ask the GDC directly. Note: only registered teams, EPs, and certified Head Refs can submit.
5. When in doubt, don't use it on the competition robot. Practice and prototype use is fine; competition use needs verified legality.

The conservative-team principle

Don't risk inspection failure for a marginal engineering benefit. A robot that doesn't pass inspection scores zero points. The hardware on this page is conservative on purpose — we use what's explicitly legal and document it for inspectors to see. Edgy parts (3D printed mounts, exotic bearings, custom plastics over the R9 limit) get tested in the lab, not at competition.

Aluminum hex threaded standoffs

The team's default replacement for VEX standoffs. ~60% lighter for the same length, same #8 thread compatibility, similar cost.

Aluminum unthreaded spacers

One long screw passes through. Stronger clamp than two-screw + standoff because there's no thread-to-thread interface that can loosen. The 7/8″ size is the centerpiece of our C-channel reinforcement technique — see Section 4.

Nylon unthreaded spacers

Identical to aluminum unthreaded spacers, but nylon. Non-conductive. Use anywhere you need to electrically isolate two metal parts — especially around the V5 brain or near sensor wiring.

When to use which

The mechanics

A 1x2x1 C-channel has three sides of metal forming a "C". Two flanges and a web. The flanges are unsupported on one edge, which means:

• The flanges can flex inward when you torque a bolt that passes through both
• The whole channel twists easily in torsion (open sections have low torsional stiffness)
• Bolts loosen over time as the metal under them yields under load

Insert an aluminum spacer inside the C-channel between the two flanges and:

• The flanges can't move toward each other — the spacer is rigid
• Torque the bolt freely — spacer takes the compression, flanges stay parallel
• The local section becomes a closed box — torsional stiffness multiplies

Why 7/8″ specifically

Build sequence

1. Identify high-load points on the C-channel: motor mounts, joint pivots, lift attachment points, anywhere that takes bending or twisting force.
2. Drill matching holes through both flanges at each reinforcement point (use VEX's standard hole grid — no custom drilling needed for VEX C-channel).
3. Slide the 7/8″ aluminum spacer between the flanges aligned with the holes.
4. Pass an 8-32 screw through both flanges and the spacer. Length needed: ~1-1/4″ (1″ flange-to-flange + 1/4″ for nut + washer).
5. Add a thread-forming locknut on the far side. Apply Loctite 242 to the thread.
6. Torque firmly but not crushingly — the spacer protects against crushing, but you don't need to over-torque.

Where the team uses this technique

Spartan applies this to high-load points only — not every hole. The pattern depends on what the C-channel does:

vs. doubling C-channels back-to-back

The "double up the C-channel" approach (recommended in some build guides) achieves similar stiffness, but:

For most uses, internal-spacer reinforcement is the right tool. Use doubled C-channels only where extreme rigidity is needed (like the very base of a tall lift tower).

Engineering notebook documentation

This is exactly the kind of design choice judges notice. Document in the notebook:

• The trade-off table (the one above)
• The math (7/8″ = 1″ − 2 × 1/16″)
• Which C-channels on the robot use the technique and which don't (with reasoning)
• Photos of the technique in use, ideally with a callout showing the spacer inside the C-channel
• R23a citation showing the part is legal

That's the kind of "competition-team-level engineering technique" entry that distinguishes a serious notebook from a basic one.

The three nut types

When to use which

Why thread-forming wins for high-cycle joints

Students disassemble robots constantly during build season — iterating, swapping motors, rebuilding subassemblies. A nut that wears out after 3–5 cycles becomes inventory waste fast.

• Thread-forming locknuts hold by deformed metal threads — the deformation doesn't fatigue with repeated use. Grip strength is consistent across 20+ cycles.
• Nylock's nylon insert is the wear part. Each install slightly deforms the nylon. After several cycles, the deformation becomes permanent and the lock action weakens.
• Cost difference is small. Thread-forming locknuts in bulk are similar price per unit to nylock from VEX.

For competition robots, thread-forming locknuts plus Loctite 242 on the screw threads is the team's recommended belt-and-suspenders approach for any joint that sees vibration.

What to cut from it

Why 6063 aluminum specifically

Architectural 6063 is the same alloy used for window frames and architectural extrusions. Properties:

• Soft enough to drill and tap easily with standard tools (no carbide bits needed)
• Strong enough for structural use at robot scale (yield strength ~25 ksi)
• Corrosion-resistant — won't rust in a school lab environment
• Lightweight — about 1/3 the density of steel
• Inexpensive — bulk 3-foot lengths cost a few dollars each

How to cut it cleanly

1. Mark the cut line with a fine-tipped permanent marker against a steel ruler.
2. Clamp the bar in a vise, leaving the cut line ~1/4″ clear of the vise jaw.
3. Cut with a hacksaw (32-tooth blade, fine cut) or a chop saw with a non-ferrous metal blade. Do not use a wood blade — teeth will catch and damage the saw.
4. Deburr the cut end with a file. Aluminum cuts leave sharp burrs; deburring takes 10 seconds and prevents finger cuts during assembly.
5. Drill holes with a drill press if possible. Use cutting fluid or a drop of dish soap; aluminum will gum up dry bits.

Legality note

Raw aluminum bar stock falls under R8 (legal raw metal stock). The team can cut and drill it as needed. Do not weld, braze, or solder it — permanent joining methods are prohibited per R7e (mechanical fasteners only). Use 8-32 screws and the standoffs/spacers from Sections 3 and 4 to attach cut pieces.

R7f — explicitly allowed

R7e — explicitly banned

Loctite 242 — the team's default

Loctite 242 is the "blue" formula — medium-strength, removable with normal hand tools. The blue bottle is the right choice for VEX use because:

• Cures in 24 hours to full strength — usable immediately, full vibration resistance overnight
• Removable — an Allen wrench can break the cured bond. Critical for student-built robots that get disassembled often.
• Works on 8-32 screws — one drop on the thread before insertion. Extra drips off; doesn't need precise application.
• Lasts indefinitely once cured — survives temperature, vibration, and humidity

Where to apply Loctite

Application technique

1. Clean the screw threads with a rag — no oil, dirt, or old Loctite residue.
2. Apply one drop to the threads about 1/4″ from the tip. Don't flood — one drop is enough for a #8 screw.
3. Thread the screw immediately while Loctite is wet. Tighten to spec.
4. Wipe off any squeeze-out with a paper towel — cured Loctite outside the threads is just a sticky mess.
5. Wait 24 hours for full cure before subjecting to heavy vibration or impact. Light handling is fine immediately.

What about other adhesives the team might consider?

Notebook documentation

For inspection, document the team's Loctite use in the engineering notebook:

• R7f citation showing threadlocker is allowed
• The brand and color used (Loctite 242, blue)
• Where on the robot it's applied (motor mounts, pivots, wheel hubs)
• Why the team uses it (reliability, prevents inter-match retightening)

Inspectors occasionally ask about visible Loctite residue on screw threads. Having the documentation ready saves time at the inspection table.

Why McMaster-Carr

• Same-day shipping from regional warehouses; most orders arrive next business day
• Free account for schools — no minimum orders, simple invoicing
• Every part in stock — not "back-ordered" or "discontinued"
• Detailed spec sheets — dimensions, materials, certifications all on the product page
• Used by professional engineers — same hardware in robotics labs and industrial settings worldwide

Verified part numbers

The single part the team has verified by McMaster SKU:

Search strings for other parts

For parts the team uses but where the SKU hasn't been individually verified, use these McMaster search terms:

Recommended order quantities (per season, 6 teams)

Order all of this together at season start. Total cost is typically under $200 for a 6-team school program — small fraction of the VEX hardware budget. Adjust quantities based on what the team consumed last season.

When to reorder mid-season

• Aluminum unthreaded spacers (7/8″): Watch consumption. If the team is doing serious C-channel reinforcement on multiple robots, 100 spacers can disappear in a month.
• Loctite: One bottle should last most of a season per team. Reorder when ~1/3 left.
• Standoffs: Generally last all season; reorder if doing major rebuilds.
• Thread-forming locknuts: Reusable, so consumption is low. 50 should last most teams.

Companion guides