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LEGO Missing Piece Checker

Rule out the usual hiding places first. If the piece really is gone, check the set piece by piece and leave with the element ID LEGO asks for, or a link to buy the part.

Checking

42666 Cat Birthday Party & Tree House

313 pieces in 138 part and color combinations, plus 2 minifigures.

The official piece count includes the 8 parts inside the set's minifigures, which this inventory lists separately. Spare parts are counted in neither figure.

Before you call it missing

Builders who report a missing piece often find it in one of these places. Tick each one off as you look.

Every bag and the box. Shake out each bag, check its corners and seams, and look inside the empty box.
Inside what you have built. Small pieces lodge inside tubes, under plates and between studs. Turn the model over and look.
The last few steps. Compare each recent step with its parts callout. A piece used in the wrong place earlier leaves you one short later.
Look-alike colors. 1 part in this set come in two colors that are easy to mix up; they are listed below.
The spare pieces. This set comes with 26 spare pieces, marked on each row of the checklist. One may be the piece you need.
The floor and your building area. Check under furniture, the chair and the edges of your building surface.

Look-alike colors in this set

These parts appear in this set in two colors that are easy to confuse. If you are one short in one color, check whether it went in where the other color belongs. Each color has its own element ID in the parts list at the back of the instructions.

Tile 1 x 2 with Groove Dark Turquoise ×2 Medium Azure ×4 Dark Turquoise is darker than Medium Azure.

Piece checklist

Bricks 25 pieces

Brick 1 x 1 Bright Light Orange Part 3005 Element 6061685 or 4490694 ×3
Brick 1 x 2 Bright Light Orange Part 3004 Element 6003003 or 4490695 ×3
Brick 1 x 1 Coral Part 3005 Element 6422915 or 6264956 ×3
Brick 1 x 2 Coral Part 3004 Element 6258572 ×3
Brick 1 x 2 Dark Orange Part 3004 Element 4579659 or 4164441 ×3
Brick 2 x 3 Dark Orange Part 3002 Element 6536259 or 4597487 ×1
Brick 1 x 1 Medium Azure Part 3005 Element 6603285 or 4619652 ×5
Brick 1 x 4 Medium Azure Part 3010 Element 6603319 or 6036238 ×2
Brick 1 x 3 White Part 3622 Element 6550143 or 362201 ×2

Bricks Round and Cones 21 pieces

Brick Round 2 x 2 Dome Bottom [Open Stud] Bright Pink Part 15395 Element 6541655 ×2
Brick Round 2 x 2 Dome Top with 2 Ears Bright Pink Part 5690 Element 6513944 or 6483520 ×2
Brick Round 1 x 1 diameter Tube with 90 Degree Elbow (2 x 2 x 1) and Axle Holes (Crossholes) at each end Tan Part 25214 Element 6541476 ×6
Cone 1 x 1 [Top Groove] Tan Part 59900 Element 4529237 ×6
Cylinder Half 2 x 4 x 4 Tan Part 6259 Element 6232142 or 6106026 ×3
Cone 1 x 1 [Top Groove] Trans-Light Blue Part 59900 Element 6514027 or 6337639 ×1
Brick Round 4 x 4 Centre Hole Yellow Part 87081 Element 6490950 or 6310222 ×1

Plates 18 pieces

Plate 1 x 4 Bright Green Part 3710 Element 6395814 or 6138515 ×2
Plate 1 x 1 x 2/3 with Open Stud Dark Orange Part 86996 Element 6382577 ×1
Plate 1 x 2 Dark Orange Part 3023 Element 4570877 or 4162217 ×5
Plate 2 x 3 Light Aqua Part 3021 Element 6426724 or 6192108 ×1
Plate 2 x 2 Light Bluish Gray Part 3022 Element 4211397 ×1
Plate 6 x 10 Lime Part 3033 Element 6289699 or 4172875 ×2
Plate 1 x 10 Medium Azure Part 4477 Element 6603595 or 6423273 ×3
Plate 2 x 4 Medium Lavender Part 3020 Element 4619516 ×1
Plate 2 x 4 Orange Part 3020 Element 4158355 or 4122468 ×2

Bars, Ladders and Fences 16 pieces

Bar 5L with Handle (Friction Ram) Black Part 87618 Element 4623113 ×1
Antenna 1 x 4 with Flat Top Dark Orange Part 3957b Element 6514016 or 6400293 1 spare in the box ×1
Bar 1L with Clip [Cut Edges and One Side Hole] [Full Clip] Reddish Brown Part 3484 Element 6439053 ×2
Bar 2L with Stop in Center Reddish Brown Part 78258 Element 6451002 1 spare in the box ×2
Bar Holder with Hole and Bar Handle Reddish Brown Part 23443 Element 6476174 ×1
Bar 2L with Stop in Center Tan Part 78258 Element 6447501 1 spare in the box ×4
Bar 2L with Stop in Center White Part 78258 Element 6357680 1 spare in the box ×1
Bar 4L (Lightsaber Blade / Wand) White Part 30374 Element 6116602 or 4129836 ×2
Bar Holder with Clip White Part 11090 Element 6341465 or 6136789 ×2

Tiles 15 pieces

Tile 2 x 3 Blue Part 26603 Element 6196596 ×2
Tile 1 x 4 with Groove Bright Green Part 2431 Element 6195267 or 4647548 ×2
Tile 2 x 2 with Groove Bright Light Orange Part 3068b Element 6020147 or 4525871 ×1
Tile 2 x 2 with Groove Bright Pink Part 3068b Element 4615728 ×2
Tile 1 x 2 with Groove Dark Turquoise Part 3069b Element 6213779 or 4164140 Also in Medium Azure ×2
Tile 1 x 2 with Cat Food Box, Cat, White 'MEOW BITS' Print Light Aqua Part 3069bpr9932 Element 6527761 ×2
Tile 1 x 2 with Groove Medium Azure Part 3069b Element 6603315 or 4649741 Also in Dark Turquoise ×4

Tiles Round and Curved 13 pieces

Tile 2 x 2 Curved, Macaroni Coral Part 27925 Element 6250024 ×2
Tile Round 1 x 2 Half Circle Medium Azure Part 1748 Element 6510074 or 6445337 1 spare in the box ×2
Tile Round 1 x 1 with Animal Track Print Medium Nougat Part 98138pr0056 Element 6287856 or 6152676 1 spare in the box ×6
Tile Round 1 x 1 Trans-Yellow Part 98138 Element 6514193 or 6274740 1 spare in the box ×1
Tile Round 1 x 1 with Offset Black Eye Print White Part 98138pr0008 Element 6284599 or 6029156 1 spare in the box ×2

Technic Connectors 11 pieces

Technic Axle Connector Hub with 3 Axles at 120° Light Bluish Gray Part 57585 Element 4502595 ×3
Large Figure Weapon Lightsaber Hilt with Axle Hole and Two Bar Holders Reddish Brown Part 24122 Element 6459423 ×2
Technic Axle Connector Smooth [with x Hole + Orientation] Tan Part 59443 Element 6262188 ×6

Minifig Accessories 10 pieces

Equipment Candlestick Black Part 37762 Element 6290456 ×1
Wool / Yarn Bright Light Yellow Part 6900 Element 6522800 ×1
Wool / Yarn Dark Pink Part 6900 Element 6509764 ×1
Equipment Shovel [Rounded Handle End] Flat Silver Part 3837 Element 6210601 or 6038687 ×1
Equipment Candlestick Reddish Brown Part 37762 Element 6422088 ×6

Bricks Special 8 pieces

Brick Special 1 x 1 with Studs on 2 Sides Blue Part 47905 Element 6531923 or 4213570 ×1
Brick Special 1 x 1 with Headlight Bright Light Blue Part 4070 Element 6387434 ×2
Brick Special 1 x 2 with 1 Center Stud on 1 Side, Bottom Stud Holder Bright Light Blue Part 86876 Element 6522315 ×1
Brick Special 1 x 2 x 1 2/3 with 4 Studs on 1 Side Dark Turquoise Part 22885 Element 6513765 ×1
Brick Special 1 x 2 with Grille Tan Part 2877 Element 4655900 or 4278250 ×3

Animals / Creatures 6 pieces

Animal, Cat, Kitten Sitting with Yellow Eyes, Dark Pink Tongue Print Black Part 69902pr0004 Element 6520727 ×1
Animal, Fish [Hollow Stud Mouth] Bright Light Blue Part 64648 Element 6195347 ×1
Animal, Cat, Chubby with Bright Green Eyes, Light Bluish Grey Fur Print Dark Bluish Gray Part 2652pr0007 Element 6542233 ×1
Animal, Cat, Sitting with Dark Brown Stripes, White Chest, Ears Print Medium Brown Part 11602pr0010 Element 6520143 ×1
Animal, Cat, Kitten Sitting with Open Eyes, White Mouth, Nougat Paws Print Nougat Part 69902pr0003 Element 6542234 ×1
Animal, Cat, Chubby with orange Face, Toes, Medium Blue/Lime Eyes Print White Part 2652pr0003 Element 6520273 ×1

Technic Axles 6 pieces

Technic Axle 2 Notched Red Part 32062 Element 4142865 ×6

Containers 5 pieces

Cupboard 2 x 3 x 2 with Hollow Studs Blue Part 92410 Element 6313992 or 4619667 ×1
Container Box 2 x 2 x 1 Reinforced Bottom Bright Light Orange Part 2821 Element 6439231 ×1
Container Box 2 x 2 x 1 Reinforced Bottom Bright Pink Part 2821 Element 6517936 ×3

Animal / Creature Body Parts 4 pieces

Animal Body Part, Barb / Claw / Tooth / Talon / Horn, Small Bright Green Part 53451 Element 6527826 1 spare in the box ×4

Minifig Headwear Accessories 4 pieces

Headwear Accessory Bow with Heart, Long Ribbon and Pin Lavender Part 11618 Element 6023826 1 spare in the box ×1
Headwear Accessory Hat with Small Pin, Cap Lime Part 6913 Element 6509777 1 spare in the box ×1
Headwear Accessory Crown / Tiara Pearl Gold Part 33322 Element 6605929 or 6173109 1 spare in the box ×1
Headwear Accessory Hat with Small Pin, Clown / Party with Pin Pearl Gold Part 24131 Element 6287612 or 6220929 ×1

Bricks Sloped 3 pieces

Brick Sloped 30° 1 x 1 x 2/3 (Cheese Slope) Bright Light Blue Part 54200 Element 6372124 1 spare in the box ×2
Brick Sloped 33° 3 x 2 Reddish Brown Part 3298 Element 4216625 ×1

Flags, Banners and Signs 3 pieces

Flag 2 x 2 Square, Flared Clip Edge [Thick Clips] White Part 80326 Element 6365487 ×3

Panels 2 pieces

Panel 1 x 2 x 3 [Side Supports / Hollow Studs] White Part 87544 Element 6550191 or 4585448 ×2

Energy Effects 1 piece

Wave / Flame Small with Pin Trans-Orange Part 37775 Element 6514274 or 6357747 1 spare in the box ×1

Hinges, Arms and Turntables 1 piece

Turntable 2 x 2 Female White Part 27448 Element 6536567 or 6238334 ×1

Plates Wedged 1 piece

Wedge Plate 2 x 4 Blue Part 51739 Element 4609454 ×1

Stickers 1 piece

Sticker Sheet for Set 42666-1 [No Color/Any Color] Part 10113040 Element 6542237 ×1

String, Bands and Reels 1 piece

String with End Studs 11L Overall Black Part 14226c11 Element 6096955 or 6037558 1 spare in the box ×1

Technic Bricks 1 piece

Technic Brick 1 x 2 [1 Pin Hole] Reddish Brown Part 3700 Element 4211252 ×1

Technic Pins 1 piece

Technic Pin 1/2 without Friction Ridges Light Bluish Gray Part 4274 Element 4274194 or 4211483 1 spare in the box ×1

Tubes and Hoses 1 piece

Hose Rigid 3mm D. 9L / 7.2cm Black Part 75c09 Element 6409912 or 4614226 ×1

Windows and Doors 1 piece

Window 1 x 4 x 3 without Shutter Tabs White Part 60594 Element 4530590 or 4520702 ×1

Minifigures 2 figures

Paisley - Bright Light Yellow Top, Medium Lavender Skirt Minifigure, checked as a whole figure ×1
Leo - Red Shirt, Yellow Shorts Minifigure, checked as a whole figure ×1

Tick each piece as you find it, or mark it missing.

When a piece really is missing

Ask LEGO

LEGO takes requests for pieces missing from a new set through its customer service site. The form asks for the set number and each piece's element ID, the number printed beside the piece in the parts list at the back of the instructions. This checker lists both.

Request a replacement from LEGO

Buy the piece

Mark a piece missing and your list links it to an eBay search for that part, which also covers pieces from older or second-hand sets.

Keep a record

Copy or download your missing list (the CSV opens in any spreadsheet), or print the whole checklist and tick pieces off on paper. Your marks stay in this browser, so you can check a big set over several sittings.