Standard vs Tight Tolerances on a Quote
What Standard and Tight Actually Mean on the Quote
Standard on an injection molding quote means the published commercial band for non-critical dimensions. Tight means extra control on named mates, seals, and snaps, not a higher quality grade for the whole part. Pick the note by the feature list, not by the word precision.
This page is the routing sheet. For the field-writing paste block and the approved size-class figures, read how to write the tolerance note on an injection molding RFQ. Do not reprint those tables here.
Standard is the commercial band for the envelope
Standard follows the published commercial table for the envelope and cosmetics. Covers, clips, hidden brackets, and branded walls usually stay here. Write that on purpose. A filename that says PREC does not change inspection.
Tight is named mates, seals, snaps, alignment pins
Tight is extra control on the faces you name: a snap, a seal, a press fit, or an alignment pin. Inspection follows that short list. If you cannot name the list, you are not ready to pick tight.
Tight is not a quality badge for the whole file
Precision molding is not a tolerance. It is a missing balloon list. Engineers often treat tight as a way to buy a better part. Procurement often treats standard as a way to keep the package simple. Both reads miss the split. Standard is the envelope. Tight is the short list. If you cannot name the list, you are not ready to pick tight.
A control-knob housing has a bearing bore, a snap to a clear lens, and a large branded wall. The bore and the snap can be tight. The branded wall can stay standard. Selecting tight for the whole file asks review to inspect cosmetics as if they were mates. That is not a quality upgrade. It is an incomplete RFQ.
Route the RFQ Instead of Rewriting the Tables
Link the live pages: commercial default, exception list, size-class table
Read standard commercial tolerance for molded parts for the commercial default. Read tight tolerances on molded mates for which mates deserve extra control. Read NetProto commercial tolerance bands for the published size-class table. Do not copy those tables into the quote.
Process routing also stops a common rewrite. Teams paste unofficial shop bands and prototype decimals into the quote because they cannot find the live pages. Those pastes become a second specification. Link the live pages. Type the face list. Leave the tables where they already live.
Write standard on the envelope, tight on these balloons
Ask sourcing to write standard on the envelope, tight on these balloons rather than picking a single dropdown for the whole part. Send the three live links with the RFQ, not a screenshot of an old chart.
A new buyer asks for precision molding on a connector housing. The engineer opens the tight-tolerances spoke, marks the pin alignment and the seal land, and leaves the body on the commercial default. The quote note then cites manufacturing standards for the envelope and lists two balloons. That package can be reviewed. A note that only says precision cannot.
When a Blank Tolerance Field Is Fine, and When It Is Not
Review will treat unspecified dimensions as commercial. That default is the published band, not a guess invented for your part. Unnamed tight decimals on a drawing still need a note so they are not missed.
Covers, clips, hidden brackets: commercial band on purpose
A blank field is workable when the part truly has no critical mate. Many covers, clips, and hidden brackets live entirely on the commercial band. Write that on purpose: all dimensions follow the commercial table on manufacturing standards. Silence is weaker than that sentence. Silence looks like a skipped field.
Snap, seal, press-fit, alignment pin: name it or it defaults to commercial
A blank field is not workable when the assembly uses a snap, a seal, a press fit, or an alignment pin. Those features will be molded to the commercial default unless you name them. If a later flag lands on that mate, follow what to do when DFM flags your part.
A lens cap is quoted with a blank tolerance field and a drawing that marks the optical seat as a tight balloon. The quote record never mentions the seat. Inspection follows the commercial default. The drawing was not wrong. The quote field never pointed at it.
RFQ Paste Block
Use these numbered steps as the paste block for the quote notes.
- Write commercial for the envelope and cosmetics.
- List each tight feature by face or balloon.
- Say why the mate, seal, or snap needs the extra control.
- Attach the drawing revision that matches the CAD revision.
- Upload CAD through the injection molding instant quote platform.
The reason line in step 3 is what keeps tight from becoming a habit. Alignment pin B locates the mating PCB is a reason. We always hold this tight is not.
A complete note looks like this: Standard: envelope and cosmetics per the commercial table on manufacturing standards. Tight: bore A (bearing seat) and snap C (lens retention) per drawing 220-revB. CAD knob_220_revB.step matches that print. That note can be inspected. Tight / quality part cannot.
If you change the band later, re-quote the same CAD revision with the new note. Do not edit a slide and leave the portal on the old selection.
Common Mistakes
Selecting tight for the whole part and attaching no mate list.
Listing ten faces as tight when two mates carry the assembly.
Assuming the filename PREC or TIGHT changes inspection. It does not.
Assuming a title block is imported automatically. It is not, unless you call it out.
Attaching a drawing from an older revision than the STEP.
Putting the why in a chat thread and leaving the notes field empty.
Review reads the quote field and the print together. If they disagree, the package is not ready for steel.