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.
Builders who report a missing piece often find it in one of these places. Tick each one off as you look.
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.
Brick Curved 2 x 1 No Studs [1/2 Bow]Black ×2Dark Bluish Gray ×2Black is darker than Dark Bluish Gray.
Brick Sloped 30° 1 x 1 x 2/3 (Cheese Slope)Black ×1Dark Bluish Gray ×2Black is darker than Dark Bluish Gray.
Technic Axle and Pin Connector PerpendicularBlack ×20Dark Bluish Gray ×4Black is darker than Dark Bluish Gray.
Technic Beam 1 x 13 ThickBlack ×5Dark Bluish Gray ×2Black is darker than Dark Bluish Gray.
Technic Beam 1 x 2 ThickBlack ×2Dark Bluish Gray ×2Black is darker than Dark Bluish Gray.
Technic Beam 1 x 2 ThinBlack ×6Dark Bluish Gray ×18Black is darker than Dark Bluish Gray.
9 more look-alike pairs
Technic Beam 2 x 4 L-Shape ThickBlack ×5Dark Bluish Gray ×6Black is darker than Dark Bluish Gray.
Technic Panel Fairing #21 5L Small Smooth, Side BBlack ×1Dark Bluish Gray ×1Black is darker than Dark Bluish Gray.
Technic Panel Fairing #22 5L Small Smooth, Side ABlack ×1Dark Bluish Gray ×1Black is darker than Dark Bluish Gray.
Technic Panel Fairing #7 3L Very Small Smooth, Side ABlack ×3Dark Bluish Gray ×4Black is darker than Dark Bluish Gray.
Technic Panel Fairing #8 3L Very Small Smooth, Side BBlack ×3Dark Bluish Gray ×4Black is darker than Dark Bluish Gray.
Technic Panel Fairing 2 x 3 x 1Black ×4Dark Bluish Gray ×9Black is darker than Dark Bluish Gray.
Technic Pin Connector Round 1L [Beam]Black ×8Dark Bluish Gray ×3Black is darker than Dark Bluish Gray.
Tile 1 x 2 with GrooveBlack ×3Dark Bluish Gray ×2Black is darker than Dark Bluish Gray.
Tile 2 x 4 with GrooveBlack ×1Dark Bluish Gray ×3Black is darker than Dark Bluish Gray.
Technic Axle and Pin Connector Perpendicular 3L with 2 Pin HolesYellowPart 42003Element 6273711 or 4200324×2
Technic Engine CrankshaftYellowPart 2853Element 6640378 or 4119474×2
Technic PistonYellowPart 4369Element 6452846×8
Orange
20 pieces
Technic Axle and Pin Connector PerpendicularOrangePart 6536Element 6261377 or 6135088×4
Technic Beam 1 x 2 Thick with Pin Hole and Axle HoleOrangePart 60483Element 6265128 or 6057526×4
Technic Beam 1 x 3 ThickOrangePart 32523Element 6102618 or 4655127×2
Technic Panel Fairing 2 x 3 x 1OrangePart 71682Element 6358255×4
Technic Pin Connector Hub with 1 Pin with Friction Ridges Lengthwise [Centered Friction Ridge]OrangePart 65487Element 6390390×2
Technic Pin Long with Friction Ridges Lengthwise and Stop Bush [2 Lateral Holes, Small Pin Hole]OrangePart 65304Element 6347790×4
Tan
13 pieces
Technic Axle Pin without Friction Ridges LengthwiseTanPart 3749Element 4666579 or 4186017×2
Technic Gear 12 Tooth BevelTanPart 6589Element 4565452 or 4514556×7
Technic Pin 3/4TanPart 32002Element 6663097 or 60139381 spare in the box×4
Reddish Brown
5 pieces
Technic Axle 3 with StopReddish BrownPart 24316Element 6135494×5
Pearl Gold
2 pieces
Technic Pin Connector Round 1L [Beam]Pearl GoldPart 18654Element 62568031 spare in the box×2
Trans-Red
2 pieces
Technic Tooth 1 x 3 with Axle Hole [Hollow Underside]Trans-RedPart 48267Element 6514318 or 6275769×2
Sand Green
1 piece
Plate 2 x 3 with 1 x 1 CutoutSand GreenPart 73831Element 6432746×1
White
1 piece
Technic Pin Connector Hub with 2 Perpendicular AxlesWhitePart 10197Element 6507770×1
[No Color/Any Color]
1 piece
Sticker Sheet for Set 42173-1[No Color/Any Color]Part 10105329Element 6462842×1
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.
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.