Scope: magnets and magnetic materials sold as crafting fasteners/closures — loose project magnets (discs/blocks/rings/spheres, neodymium or ceramic/ferrite), flexible magnetic sheet/roll/tape, and magnetic clasps/closures for jewelry and sewing. Excludes magnetic paint (Paints, Inks & Dyes leaf) and non-magnetic hook-and-loop fasteners.

Seed:
1. magnet_material is the trade-off axis: push pull-force-per-volume up with neodymium and you gain holding strength but give up the corrosion resistance, heat tolerance and low cost that ceramic/ferrite keeps (kjmagnetics_safety, wikipedia_neodymium).
2. A ship's cook (humid, salty, no climate control) would notice first that nickel-plated neodymium corrodes and loses strength in damp/salt air, and would reach for ceramic/ferrite or rubber/epoxy-coated magnets over bare nickel-plated ones even at the same pull force (wikipedia_neodymium, kjmagnetics_safety).

Sources:
[kjmagnetics_specs] https://www.kjmagnetics.com/neodymium-magnet-specifications.asp — N35–N52(+M/H/SH/UH/EH/AH) grade table (Br, Hci, BHmax) and thermal table (N=176°F/80°C, NM=212°F/100°C, NH=248°F/120°C) — fetched excerpt
[kjmagnetics_safety] https://www.kjmagnetics.com/neodymium-magnet-safety.asp — pinch/crush injury, choking hazard for children, pacemaker/ICD interference, brittle/shatters, nickel-copper-nickel plating standard but not waterproof, nickel allergy, flammable dust — fetched excerpt
[kjmagnetics_grades_blog] https://www.kjmagnetics.com/blog/magnet-grade — letter prefix meaning: N=neodymium, C=ceramic, SmCo=samarium cobalt; number = BHmax in MGOe — fetched excerpt
[wikipedia_neodymium] https://en.wikipedia.org/wiki/Neodymium_magnet — strongest commercial permanent magnet, remanence ~1.3T; grades N28–N55 with M/H/SH/UH/EH/TH temp-suffix system; coatings nickel/nickel-copper-nickel/zinc/polymer/lacquer; pinch and shatter hazards — fetched excerpt
[wikipedia_ferrite] https://en.wikipedia.org/wiki/Ferrite_magnet — hard ferrite (ceramic) magnets cheap, corrosion-resistant, brittle ceramic, max B ~0.35T, used in fridge magnets — fetched excerpt
[wikipedia_magnet] https://en.wikipedia.org/wiki/Magnet — flexible magnet = ferrite powder in polymer binder extruded as sheet, magnetized in alternating N/S stripes, lower strength but flexible; alnico max usable temp >540°C vs ferrite/SmCo ~300°C vs NdFeB ~140°C — fetched excerpt
[wikipedia_buckyballs] https://en.wikipedia.org/wiki/Buckyballs_(toy) — CPSC regulatory history on small high-powered sphere magnets, ingestion injuries, 2012 rule vacated 2016, advisory against under-14 use — fetched excerpt

Branches:
- form_factor=raw_magnet → ask magnet_material, neodymium_grade, heat_rating_suffix, shape, coating_finish, mount_feature, pull_force_class (kjmagnetics_specs: grade/thermal tables apply to loose magnets, not sheet or clasp).
- form_factor=flexible_sheet_or_tape → ask form_cut, adhesive_backing, printable_surface, best_holding_surface; material is fixed to bonded_flexible_ferrite (wikipedia_magnet: flexible magnet = ferrite-in-binder sheet), so magnet_material/grade/heat-suffix become irrelevant.
- form_factor=clasp_or_closure → ask clasp_mechanism, locking_mechanism, strand_capacity, closure_scale; shape/mount_feature/form_cut become irrelevant (kjmagnetics nav: clasps sold as "magnetic closures," a distinct product line from bare shaped magnets).
- magnet_material=neodymium → ask neodymium_grade, heat_rating_suffix (kjmagnetics_specs tables only apply to NdFeB); ceramic_ferrite/alnico make those two irrelevant (wikipedia_ferrite has no N-grade system).
- primary_use=jewelry_or_sewing_closure → nulls pull_force_class only; form_factor=clasp_or_closure already owns clasp_mechanism/locking_mechanism, so this branch doesn't re-ask them.
- primary_use=mounting_or_hanging → ask pull_force_class, mount_feature (these matter only once the buyer's job is mounting/hanging, not decor or a closure).

Noise (spec-sheet rows left out):
- Exact magnet dimensions (diameter/thickness in mm or inches) — purely a per-SKU listing field, not an expert judgement call; every K&J product varies continuously.
- Price per magnet / price per roll — price is never a facet per house rules.
- Brand/manufacturer name — never a facet per house rules.
- IATA air-shipping magnetism restrictions (kjmagnetics_safety mentions these) — a shipping/logistics compliance detail for sellers, not a buyer-facing product attribute.
- Nickel-allergy skin reaction note (kjmagnetics_safety) — folded into safety_hazard_profile rather than a separate facet; too narrow to stand alone.
- "Color" (Silver/Gold/Dark Gray filter on K&J's brand page) — the visible result of coating_finish (nickel-plated=silver, gold-plated=gold, epoxy/black-oxide=dark gray), not a separate attribute.

Corrections (2026-10-26):
- heat_rating_suffix AH value was 230°C (conflated with wikipedia's separate TH suffix); fixed to 220°C per kjmagnetics_specs's own thermal table (NAH = 428°F/220°C), also fixed in mechanism.plain, magnet_material.why_experts_care, and the neodymium/ferrite tradeoff.
- neodymium_grade.why_experts_care's "N52 is roughly 30% stronger than N35" recomputed from kjmagnetics_specs BHmax (N35 33-35 MGOe, N52 49.5-52 MGOe) to "~49% more maximum energy product (BHmax)".
- primary_use.values already included science_or_education but it was missing from the cold_start_question/split question; added it so the value is reachable.
- Removed the duplicate then_ask (clasp_mechanism, locking_mechanism) from primary_use's jewelry_or_sewing_closure branch; form_factor=clasp_or_closure is now the sole split that asks those two, primary_use only nulls pull_force_class on that path. Logged both primary_use branches above (previously missing).
- Added coating_finish to form_factor=clasp_or_closure's makes_irrelevant (sibling sheet branch already nulled it; clasp path left it dangling).
- clasp_mechanism and strand_capacity cited kjmagnetics_specs/kjmagnetics_safety, but neither page contains "strand," "barrel," or any clasp-shape term (confirmed by grep on a fresh fetch). Re-sourced both to [fmg_magclasps] (Fire Mountain Gems' magnetic-clasps listing page), which has a real "Number of Holes/Loops" strand filter (1/2/3/4-strand) and real SKU names for barrel, round, oval, double-ball and fold-over clasps. clasp_mechanism's values were rewritten to match the shapes actually sold (barrel_two_piece, round_or_oval, fold_over, double_ball, other_shape); ball_and_socket/hidden_box_snap/slide_tube were invented and are dropped.
- locking_mechanism and closure_scale had the same fabricated kjmagnetics citations with no real replacement found this session (no safety-chain or size-tier language on the fetched clasp listing page). Evidence cleared to [], source changed to researched, backfill_cost raised to medium, and backfill_note now says the field is unconfirmed this session rather than claiming it as a stated listing field.
- Added vocabulary entries for "remanent field" (remanence, linked to magnet_material) and "maximum energy product" (BHmax, linked to neodymium_grade), both used undefined in facet prose.
- Fetched kjmagnetics' real "Magnetization Directions" page (magdir.asp): disc/cylinder/ring magnets can be axially or diametrically magnetized, blocks through thickness. Added a new magnetization_direction facet (axial/diametric/through_thickness) sourced to it, covering the brand page's real "Magnetization Direction" filter row the original register had no facet for.
- Judgement on CPSC status: added that a 2020 CPSC petition response proposed a 2022 rule vote with no later text showing one adopted, confirming "unsettled" rather than a hard current limit (same wikipedia_buckyballs source, re-grepped).
- Rejected: checker's claim that magnet_material's "1 to 1.5 T" neodymium remanence range isn't verbatim anywhere. Re-fetched wikipedia_neodymium and grepped it directly: its Neodymium-vs-Sm-Co properties table states "Remanence (T) 1-1.5" for neodymium verbatim, alongside the separate "typically 1.3 teslas" prose sentence the checker found. The range is real and sourced; left unchanged.