Notes: No transparent parts are included in any category except categories 10-13, 17, 24, and 35. and Any measurement denoted with an asterisk (*) means that the particular measurement can be any number. The images below each category are merely visual aids, with EXAMPLES of parts found in each category; the categories do not necessarily consist only of the parts in the images.
Here are the standard parts and pieces that are essential to every LEGO builder’s collection.
Category 1: Small Bricks & Plates
As the name dictates, this includes any small standard LEGO brick or plates. It includes bricks no bigger than 1×2, with the exception of 2×2 corner bricks (including rounded corner bricks). No brick is higher than 1 brick high. It also includes plates no wider than 1 stud, and no longer than 5L. It has any 1×2 bricks w/ pins, pin holes, or axle holes also. Also 1×2 plates w/ rails on sides.
Category 2: Medium Plates
Only standard 1/3 h plates make up this category. It includes any 2w plate (any length), and any 1w plate (any plate longer than 5L). Angled plates no wider that 2w are also in this category, as well as 2×2 round plates. Also plates w/ rails on sides, and 2×2 bottom round dishes. Excludes plates in Category 10.
Category 3: Large Plates
This includes the rest of the 1/3 h plates. It includes angled plates, round plates, and car chassis w/o pins.
Min. Plate size: 3x3x1/3
Category 4: Bricks
This includes all standard bricks not included in Category 1. Any brick that has as many studs on top as it has stud holes on the bottom is included in this category: window and door frames, bricks w/ axle or pin holes, bricks w/ pins, round bricks, panel bricks, sliding rail bricks, etc. Among more unusual large bricks, it has large rock sections, staircase bricks (not including the spiral staircase step pieces), and castle bricks. Note: though it does include both panel bricks and round bricks, the semi-round panel bricks are not included (see category 13).
Category 5: Slope Bricks
This includes any roof brick or slope, with at least one stud on top and one stud hole on bottom, but an equal number of both. Inverted slopes, standard slopes, wedge slope bricks, etc. are all included, as well as ridged tiles. Exceptions include any roof bricks or slope tiles mentioned in any category below.
Category 6: Wheels
Any and all wheels, tires, and tank tread parts go here.
Category 7: Technic Parts
This includes any technic liftarms, technic panels, technic ball joint balls, liftarms w/ ball joint balls, bushes, gears, pin & axle joiners, and small Bionicle torso parts. It also excludes Technic launchers (see Category 32).
Category 8: Pins & Axles
This includes any and all pins and axles. Due to sheer length, the rare 32L axle I have in my collection was not included in this category, but was included in Category 37.
Category 9: Minifigure Parts & Accessories
This includes any and all minifigure parts and accessories, including any 4L or 3L bar, accessory w/ a bar attachment of any kind, helmets, visors, any part that attaches to a minifigure neck, torso, or legs, hair pieces, and ski pieces. Exceptions include any part w/ bar mentioned in Category 23 or 35. It also includes any bricks, tiles, roof bricks, etc. with sticker or printed detail related to instruments or tools used by minifigures.
Category 10: Small Transparent Plates & Small Transparent Bricks
This includes any and all transparent plates, and small transparent Bricks (same definition as Category 1).
Category 11: Transparent Tiles
This includes any and all transparent tiles.
Here are the categories that are common among slightly larger and more varied part collections.
Category 12: Transparent Bricks
This includes any and all transparent bricks and roof bricks.
Category 13: Large Panels/Canopies
This includes transparent and non-transparent vehicle canopies, cockpit covers, dome pieces, semicircle panel bricks, etc.; any hollow slope brick or piece, and hollow brick at least 2w.
Category 14: Vehicle Parts
This includes anything related to vehicles and vehicle controls: engines, chassis (except chassis plates), steering wheels and columns, levers, propellers, propeller frames, propeller blades, spoilers, fins, fenders, common vehicle styling parts, etc.
Category 15: 1w Tiles
This includes any and all non-transparent tiles that are 1w.
Category 16: Large Tiles
This includes any and all non-transparent tiles bigger than 1w.
Category 17: Dishes
This includes any dish parts, without bottom dishes.
Category 18: Large Figure Body Parts
This includes any Bionicle, Hero Factory, Knight’s Kingdom, ultrabuild, etc. heads, hands, arms, legs, torsos, etc. of large figure sets.
Category 19: Large Figure Armor Pieces
This includes any Bionicle, Hero Factory, Knight’s Kingdom, ultrabuild, etc. armor pieces, masks, feet, and capes.
Category 20: Large Figure Weapons
This includes any Bionicle, Hero Factory, Knight’s Kingdom, ultrabuild, etc. weapons, including claws, blades, shields, projectile launchers (except those included in Category 32), projectiles (except those included in Category 32), etc.
Category 21: Floral & Natural Décor
This includes flowers, tree leaves, vines, and related greenery.
Category 22: Tubes & Wires
This includes all tubes & long, flexible parts, with no part with a circumference more than 1 brick.
Category 23: Connectors
This is a very broad category with SNOT bricks, bars longer than 4L, brackets, dinosaur tail ends, pieces w/ clips, hinges, turntables, pieces w/ bars, T-shape bars, etc. plus Bricks w/ Sockets.
Category 24: Windows & Doors
This includes any and all windows and doors.
Category 25: Grates & Cages
This includes any and all gates, cages, lattices, fences, etc.
Category 26: Rubber Bands
This includes any and all rubber bands.
Category 27: Small Panels
This includes all *x1x1 Panel bricks.
Now we come to the slightly more uncommon categories, composed of fewer part types.
Category 28: 2/3h Slopes
The 1x*x2/3 slopes (a.k.a. “cheese wedges”) and 1x2x2/3 Slopes w/ Lattice are in this category, except for Ridged Tiles
Category 29: Smooth Slopes w/o Studs
This includes any and all slopes without studs, except for Ridged Tiles. Includes Bricks w/ Bow pieces.
Category 30: Plates w/ Pin Holes
All plates with pin holes are in this category, including catapult pieces, technic beams w/ antistud parts, and coupling plates.
Category 31: Plates w/ Pins
All plates and tiles with pins are included, with chassis plates, in this category.
Category 32: Launchers
This includes all brick-based launchers, as well as Technic-based launchers, and their projectiles. Exceptions include all launchers used in Large Figure sets.
Category 33: Arch Bricks
This includes all arch bricks, with the arched window frames.
Category 34: Large Creature Parts
This includes all large creature parts and the creatures’ accessories; such as dinosaurs, horses, cows, Star Wars creatures, etc.
Category 35: Jewels & Valuables
This includes all gems, crystals, coins, and gold- or silver-chrome colored parts (except those in Category 9).
Category 36: Chains & Ropes
This includes all chains, ropes, and strings, as well as string reels and their bases.
Category 37: Assorted Parts
This includes any parts that currently do not belong to any category, or are in insufficient quantity to form a category.