BlockTalk Find Your Set

Free tool

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.

Mechanical Engineering Set

Checking

9665 Mechanical Engineering Set

322 pieces in 84 part and color combinations.

LEGO counts 318 pieces. This inventory comes from a separate parts catalog and lists 322; the two do not always count the same elements, so their totals differ. 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.

Show

Piece checklist

Technic Pins 66 pieces

  • Technic Pin with Friction Ridges Lengthwise and Center Slots Black Part 2780 Element 4121715 or 278026 ×24
  • Technic Pin 3/4 Dark Gray Part 32002 Element 4109854 ×8
  • Technic Axle Pin without Friction Ridges Lengthwise Light Gray Part 3749 Element 4184168 or 4154179 ×12
  • Technic Pin 1/2 without Friction Ridges Light Gray Part 4274 Element 427402 ×4
  • Technic Pin without Friction Ridges Lengthwise Light Gray Part 3673 Element 4184166 or 367302 ×18

Technic Bushes 36 pieces

  • Technic Bush Light Gray Part 3713 Element 4125313 or 659002 ×24
  • Technic Bush 1/2 Smooth with Axle Hole Reduced Light Gray Part 32123a ×12

Technic Bricks 30 pieces

  • Technic Brick 1 x 12 [11 Pin Holes] Blue Part 3895 Element 389523 ×4
  • Technic Brick 1 x 16 [15 Pin Holes] Blue Part 3703 Element 370323 ×6
  • Technic Brick 1 x 2 [1 Pin Hole] Blue Part 3700 Element 370023 ×8
  • Technic Brick 1 x 4 [3 Pin Holes] Blue Part 3701 Element 370123 ×4
  • Technic Brick 1 x 6 [5 Pin Holes] Blue Part 3894 Element 389423 ×4
  • Technic Brick 1 x 8 [7 Pin Holes] Blue Part 3702 Element 370223 ×4

Plates 28 pieces

  • Plate 1 x 10 Light Gray Part 4477 Element 447702 ×4
  • Plate 1 x 2 Light Gray Part 3023 Element 302302 ×4
  • Plate 1 x 4 Light Gray Part 3710 Element 371002 ×4
  • Plate 1 x 8 Light Gray Part 3460 Element 346002 ×4
  • Plate 2 x 2 Light Gray Part 3022 Element 302202 ×2
  • Plate 2 x 6 Light Gray Part 3795 Element 379502 ×2
  • Plate 6 x 8 Light Gray Part 3036 Element 303652 or 303602 ×1
  • Plate 1 x 2 Yellow Part 3023 Element 302324 ×7

Technic Gears 27 pieces

  • Technic Worm Gear Black Part 4716 Element 6037533 or 471626 ×2
  • Technic Gear Differential, 24 -16 Tooth with Clutch on Both Sides Dark Gray Part 6573 Element 657327 ×1
  • Technic Gear 12 Tooth Double Bevel Green Part 32270 Element 4144370 ×2
  • Technic Gear 20 Tooth Double Bevel with Axle Hole Type 2 [X Opening] Green Part 32269 Element 4144369 ×2
  • Technic Gear 12 Tooth Bevel Light Gray Part 6589 Element 658902 ×4
  • Technic Gear 16 Tooth with Round Holes [Old Style] Light Gray Part 4019 Element 4107176 or 401902 ×2
  • Technic Gear 24 Tooth Crown with Reinforcements [New Style] Light Gray Part 3650c Element 365002 ×2
  • Technic Gear 24 Tooth [New Style with Single Axle Hole] Light Gray Part 3648b Element 4107543 or 364802 ×2
  • Technic Gear 8 Tooth Light Gray Part 3647 Element 364702 ×3
  • Technic Gear Rack 1 x 14 with Holes Light Gray Part 32185 Element 4124442 ×2
  • Technic Gear Rack 1 x 4 Light Gray Part 3743 Element 374302 ×2
  • Technic Gear 40 Tooth Red Part 3649 Element 4120108 ×2
  • Technic Gear 24 Tooth Clutch with Dark Gray or Light Gray Center White Part 76019 Element 4270486 ×1

String, Bands and Reels 25 pieces

  • Rubber Band Medium (Square Cross Section) Thin Cut Black Part 70012 Element 70012 ×9
  • String Cord Thin (0.5mm) 500cm Black Part 56823c500 Element 4276327 ×1
  • Technic Rubber Belt Medium [26mm ID] [Round Cross Section] Blue Part 85545 Element 6049730 or 4544147 ×5
  • Technic Rubber Belt Medium [24mm ID] [Round Cross Section] Red Part 85544 Element 4544145 or 4544143 ×5
  • Technic Rubber Belt Large [33mm ID] [Round Cross Section] Yellow Part 85546 Element 4544151 or 70905 ×5

Technic Axles 22 pieces

  • Technic Axle 10 Black Part 3737 Element 373726 ×2
  • Technic Axle 12 Black Part 3708 Element 370826 ×2
  • Technic Axle 2 Notched Black Part 32062 Element 4109810 or 3206226 ×4
  • Technic Axle 3 Black Part 4519 Element 6238084 or 451926 ×2
  • Technic Axle 4 Black Part 3705 Element 370526 ×4
  • Technic Axle 5 Black Part 32073 Element 4114740 ×2
  • Technic Axle 6 Black Part 3706 Element 370626 ×2
  • Technic Axle 8 Black Part 3707 Element 370726 ×2
  • Technic Axle 3 with Stud Dark Gray Part 6587 Element 4113884 or 658727 ×2

Wheels and Tyres 22 pieces

  • Technic Wedge Belt Wheel Tire Black Part 2815 Element 6028041 or 281526 ×2
  • Tyre 30 x 10.5 Offset Tread Black Part 2346 Element 234676 or 234626 ×4
  • Tyre 43 x 17 Black Part 3634 Element 4523564 or 363426 ×2
  • Tyre Offset Tread 24 x 8 Black Part 3483 Element 4501048 or 348326 ×2
  • Technic Wedge Belt Wheel [aka Pulley] Light Gray Part 4185 Element 4100502 or 418502 ×2
  • Wheel with Split Axle hole Yellow Part 3482 Element 348224 ×10

Plates Special 16 pieces

  • Plate Special 1 x 2 with Door Rail Light Gray Part 32028 Element 4109642 ×4
  • Technic Plate 2 x 4 [3 Holes] Light Gray Part 3709 Element 370902 ×8
  • Technic Plate 2 x 8 [7 Holes] Light Gray Part 3738 Element 373802 ×4

Bricks 8 pieces

  • Brick 2 x 4 Blue Part 3001 Element 300173 or 300123 ×8

Electronics 8 pieces

  • Wire with Brick 2 x 2 x 2/3 Pair, 15L Black Part 5306bc015 Element 75565 ×1
  • Wire with Brick 2 x 2 x 2/3 Pair, 69L Black Part 5306bc069 Element 75782 ×2
  • Battery Box, 9V 4 x 14 x 4 with Dark Gray Base [Complete Assembly] Light Gray Part 2847c01 Element 4109813 or 74650 ×1
  • Motor Pulley, 9V Micromotor with axle hole Light Gray Part 2983 Element 298630 ×2
  • Motor, 9V Mini [Old Style] Light Gray Part 71427c01 Element 4107786 ×1
  • Pole Reverser / Polarity Switch with Center Part [Complete Assembly] Light Gray Part 6551c01 Element 75214 ×1

Technic Special 7 pieces

  • Technic Link 1 x 11 Blue Part 6247 Element 624723 ×4
  • Technic Cam Light Gray Part 6575 Element 657502 ×2
  • Technic Gearbox 2 x 4 x 3 1/3 Trans-Clear Part 6588 Element 6507887 or 6254290 ×1

Tiles 6 pieces

  • Tile 1 x 4 with Groove Blue Part 2431 Element 243123 ×2
  • Tile 1 x 8 with Groove Blue Part 4162 Element 416223 ×2
  • Tile 1 x 2 with Groove Yellow Part 3069b Element 306924 ×2

Pneumatics 4 pieces

  • Pneumatic Switch with Top Studs Light Gray Part 75215 Element 4190775 or 75215 ×1
  • Pneumatic Cylinder 1 x 5 with 2 Inlets Yellow Part 74981 Element 6005292 or 4625540 ×1
  • Pneumatic Pump 1 x 5.5 Yellow Part 74982 Element 4563137 or 74982 ×2

Technic Beams 4 pieces

  • Technic Beam 1 x 4 Thin with Stud Connector Light Gray Part 2825 Element 4107133 or 282502 ×2
  • Technic Beam 1 x 5 Thin Light Gray Part 32017 Element 4106885 ×2

Technic Connectors 4 pieces

  • Technic Axle Connector Ridged [with x Hole x Orientation] Light Gray Part 6538b Element 4113804 or 4100408 ×4

Gear Parts 3 pieces

  • Storage Bin, Dacta, Small Red Part upn0032 ×1
  • Storage / Sorting Tray, Dacta, 40 Compartment for Dacta Small Bin Trans-Clear Part 4132168 ×1
  • Storage Bin Lid, Dacta, 19 x 24 Trans-Clear Part 71082 ×1

Tubes and Hoses 3 pieces

  • Hose, Pneumatic 4mm D. 26.25L / 21cm Black Part 5102c26.25 ×1
  • Hose, Pneumatic 4mm D. 20L / 16cm Blue Part 5102c20 Element 6449538 ×1
  • Hose, Pneumatic 4mm D. 26.25L / 21cm Light Gray Part 5102c26.25 ×1

Bricks Round and Cones 2 pieces

  • Brick Round 2 x 2 with Axle Hole Yellow Part 3941 Element 614324 or 394124 ×2

Technic Steering, Suspension and Engine 1 piece

  • Technic Steering Pulley Large Light Gray Part 3736 Element 373602 ×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.

We value your privacy

We use cookies 🍪 for analytics and to improve your experience. Read our privacy policy