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.
Brick 2 x 2 CornerBlackPart 2357Element 235776 or 235726×2
Brick Curved 1 x 4 x 1 1/3 No Studs, Lowered Inside SupportBlackPart 6191Element 4200031×4
Brick Round 4 x 4 with 4 Side Pin Holes and Center Axle HoleBlackPart 6222Element 6533083 or 4290056×1
Brick Special 1 x 1 with HeadlightBlackPart 4070Element 407026×4
Flexible Hose 8.5L with Tabbed Ends (Ends same color as Tube)BlackPart 73590c02aElement 4540890 or 621130×3
Hinge Brick 1 x 2 BaseBlackPart 3937Element 393726×17
Plate 1 x 6BlackPart 3666Element 366626×2
Plate 4 x 12BlackPart 3029Element 302926×2
Plate 4 x 6BlackPart 3032Element 303226×1
Plate Round 1 x 1 with Solid StudBlackPart 6141Element 6141262 spares in the box×20
Plate Special 1 x 1 with Clip Vertical [Thick U Clip]BlackPart 4085cElement 408526×2
Plate Special 2 x 2 with 1 Pin Hole [Split Underside Ribs]BlackPart 2444Element 244426×2
Technic Axle 2 NotchedBlackPart 32062Element 4109810 or 3206226×5
Technic Axle 4BlackPart 3705Element 370526×1
Technic Axle 6BlackPart 3706Element 370626×2
Technic Axle 8BlackPart 3707Element 370726×5
Technic Axle and Pin Connector Angled #6 - 90°BlackPart 32014Element 6268905 or 4107767×4
Technic Brick 4 x 4 with 2 x 2 OpeningBlackPart 32324Element 6222427 or 4226981×2
Technic Pin Long with Friction Ridges Lengthwise, 2 Center SlotsBlackPart 6558Element 655826×26
Technic Pin with Friction Ridges Lengthwise and Center SlotsBlackPart 2780Element 4121715 or 2780263 spares in the box×55
Technic Plate 2 x 4 [3 Holes]BlackPart 3709Element 370926×8
Technic Plate 2 x 6 [5 Holes]BlackPart 32001Element 3200126×1
Tile 1 x 8 with GrooveBlackPart 4162Element 416226×12
Turntable 4 x 4 Top, LockingBlackPart 30658Element 4142915×1
Blue
56 pieces
Technic Axle Pin with Friction Ridges LengthwiseBluePart 43093Element 4309323 or 4206482×14
Technic Pin 1/2 without Friction RidgesBluePart 4274Element 41430053 spares in the box×41
Technic Rubber Belt Medium [26mm ID] [Round Cross Section]BluePart 85545Element 6049730 or 4544147×1
Tan
18 pieces
Technic Brick 1 x 4 [3 Pin Holes]TanPart 3701Element 4234365 or 370105×18
Red
4 pieces
Brick Sloped 33° 3 x 2RedPart 3298Element 329821×4
[No Color/Any Color]
1 piece
Sticker Sheet for Set 10174-1[No Color/Any Color]Part 56143Element 4293490×1
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.