Acetal (POM)
- Stable length in humid environments
- Good for precision stack height
- Lower impact than nylon
Molded part guide: spacers
Injection Molded Spacers
A spacer sets distance between two parts on a bolt or shaft. Molded spacers are cheap at volume, but a tall thin tube warps and a tight clearance hole binds when shrink is ignored.
Distance
Height is the tolerance that matters
Spacers show up in valve stacks, motor mounts, and electronics assemblies. They can be plain tubes, shouldered rings, or square blocks with a through hole. The stack height is the sum of spacer length plus mate part thicknesses plus bolt head clearance.
Through holes are clearance for the screw shank, not thread forming. If the hole is too tight at minimum plastic, assembly binds. If too loose, the stack rocks.
Shoulder spacers locate a bearing or a pulley on a shaft with one molded step. The shoulder face must be square to the bore so the seated part does not tilt.
Forms
Common spacer shapes
| Shape | Use | Molding note |
|---|---|---|
| Plain tube | Bolt stack height | Core supported for length; watch end flatness |
| Shoulder ring | Axial location on shaft | Step must be moldable without collapsing core |
| Square block spacer | Anti-rotation in stack | Corner radii reduce stress and help fill |
Resin
Acetal for stability or nylon for toughness
Nylon
- Better for bumped assemblies
- Length changes with moisture
- Glass fill stiffens long tubes
Drawing
Spacer quote inputs
Overall length and shoulder heights if any
Through hole diameter and clearance class for the fastener
Stack tolerance budget with mate parts
Load: compression only or side load on the tube
Flatness needs on end faces
Quantity and whether multiples fit in one mold
Keep reading
Related guides
Standoffs
Board height posts.
StandoffsBushings
Sliding sleeves, not stack rings.
BushingsTolerance stack up
Stack height at extremes.
Tolerance stack upAcetal (POM)
Stable spacer resin.
Acetal (POM)Warpage
Tall tubes bowing.
WarpageMounting brackets
Spacers in bolted plates.
Mounting bracketsStandard tolerances
Length and hole callouts.
Standard tolerancesGears
Shoulder spacers on shafts.
GearsMolded parts hub
Every part-type guide.
Molded parts hubFAQ
Questions about molded spacers
Can one mold run many spacer lengths?
Family molds are possible when lengths share the same bore and OD system. Each length is a separate cavity and adds tool cost.
Our stack height varies part to part.
Check length at tolerance extremes plus mate parts. Acetal spacers often reduce humidity drift compared with nylon.
Is threading the ID ever molded?
Internal threads are possible on larger bores with unscrewing cores. Small clearance holes stay smooth for shank clearance.
Can spacers be clear polycarbonate?
Yes when visibility matters. Clear resins need even wall and careful gate choice to avoid flow marks in the bore.
Next step
Quote the spacer with stack tolerances
Upload CAD with length, hole, and mate parts in the stack. DFM feedback covers core support and end face flatness.