MIL-PRF-13830B governs the manufacture, assembly and inspection of finished optical components such as lenses, prisms and mirrors, and its section 3.5 defines surface quality as a visibility grade rather than a measured width. Scratch and dig numbers describe how a defect looks against a comparison set, not how wide it is in micrometres. Engineers writing procurement documents should always name the comparison standard drawing and the inspection conditions, or specify ISO 10110-7 when a dimensional limit is genuinely required.
TL;DR:
- Scratch and dig grades are based on visibility against a master comparison set, not fixed defect widths measured in microns.
- Inspection conditions such as lighting, viewing angle, and the comparison standard brand significantly influence defect visibility and acceptance results.
- A clear procurement clause must specify the exact MIL-PRF-13830B revision, clause 3.5, comparison standard, lighting, magnification, and sampling method to prevent disputes.
- High-brightness or high-resolution optics may require a dimensional defect size limit from ISO 10110-7 instead of visual scratch and dig grading.
- The current official status of MIL-PRF-13830B can be confirmed via the DLA ASSIST portal, ensuring compliance with the latest revision and notices.
Table of Contents
- What the specification covers and how to check its current status
- How scratch and dig grading works and how to read the numbers
- Inspection and verification: practical setup and acceptance practice
- Limitations of scratch and dig and practical alternatives
- How to write unambiguous procurement clauses referencing MIL-PRF-13830B
- Applying the standard in production: Precision Glasses’ approach
- Author perspective: best-practice recommendations from an optics manufacturer
- How Precision Glasses can help deliver MIL-PRF-13830B compliant parts
- Sources
- FAQ
What the specification covers and how to check its current status
MIL-PRF-13830B applies to finished optical components used in fire control and related instruments: lenses, prisms, mirrors, reticle windows and wedges. It sets requirements for the optical, mechanical and cosmetic quality of these parts once fabrication is complete, and it ties acceptance to inspection methods rather than to a particular polishing or grinding process.
Because a performance specification like this is periodically reviewed, confirm the active revision before quoting it on a drawing. The ASSIST-QuickSearch entry for MIL-PRF-13830 lists the document status, issue date and next review date, and it is the authoritative source for current status and notices.
A few practical points for engineering teams checking status:
- Treat the DLA/ASSIST listing as the reference copy; other hosts are convenience libraries.
- Watch for notices (commonly labelled notice-2, notice-3 and so on), which amend or reinstate parts of the base document without replacing the whole specification.
- Download PDFs from ASSIST or from a library such as EverySpec, which hosts MIL-PRF-13830B and its notices as a mirrored copy, though ASSIST remains the authority for formal status.
How scratch and dig grading works and how to read the numbers
Section 3.5 of MIL-PRF-13830B does not measure defects with a gauge. It compares each scratch or dig against a master comparison set, historically tied to drawing C7641866, and assigns a grade based on how visible the defect appears under set conditions. A “60-40” callout, for example, means the worst scratch must look no more visible than the number 60 reference scratch, and the worst dig no larger than the number 40 reference dig, when viewed side by side with the comparison set.
That comparison basis is the source of most disputes on the shop floor. The process typically runs like this:
- Place the comparison standard and the part under inspection together under the specified illumination.
- View both at the stated angle and distance, using the naked eye or the magnification stated on the drawing.
- Judge whether the part’s worst scratch and dig are less visible than, equal to, or more visible than the reference features on the standard.
- Record a pass or fail against the callout, noting the specific defect location on the part.
Statistic callout: the scratch-and-dig standard is a visibility comparison method using a master set, not a micrometre width measurement, which means two labs can reach different verdicts on the same part if they use different comparison hardware.
The most common misconception is treating a scratch number as if it corresponds to a fixed width in microns. It does not: the grade depends on scratch morphology, light scatter and the brightness of the comparison set itself. Historical revisions to the comparison drawing have added to the confusion, which is why drawings that omit the comparison standard brand invite inconsistent acceptance decisions between supplier and customer.
Inspection and verification: practical setup and acceptance practice
A repeatable scratch and dig inspection depends more on bench discipline than on any single instrument. The comparison method calls for controlled, consistent viewing conditions every time a part is checked, whether that inspection covers one lens or an entire batch.
A workable bench setup typically includes:
- A darkfield or grazing-incidence light source, since scratches and digs scatter light differently from the surrounding polished surface.
- A fixed viewing distance and angle, matched to the magnification stated on the drawing or RFQ.
- The comparison standard mounted alongside the part, never substituted with a photograph or a description.
- A documented pass/fail record that references the exact clause and callout used for the decision.
Acceptance practice varies with contract requirements. Some programmes call for 100% visual inspection of finished optics, particularly for defence and aerospace parts where a single rejected unit can hold up an assembly; others accept a sampling plan agreed in advance with the customer. Coated surfaces, cemented assemblies and edge chips are usually treated as separate defect categories with their own acceptance limits, since a scratch on an anti-reflection coating is not equivalent to one on bare glass.
Pro Tip: record the comparison standard brand, the operator’s name, the inspection date and the batch number on every certificate, so a disputed part can be traced back to the exact conditions under which it was judged.
Limitations of scratch and dig and practical alternatives
Visibility grading works well for conventional optical systems where a cosmetic defect only scatters a small amount of stray light. It becomes a poor fit for high-resolution sensor optics or high-brightness laser systems, where a defect invisible to the eye against a comparison set can still degrade image contrast or damage a coating under intense illumination.
For those cases, a dimensional approach gives an objective limit instead of a subjective comparison:
- ISO 10110-7 specifies surface imperfections by a root area calculation, giving a maximum permissible defect size independent of any comparison hardware.
- Some procurement approaches, informally following OP1.002-style practice, blend the two systems: MIL-PRF-13830B for general cosmetic acceptance, with a dimensional override on function-critical zones.
A workable hybrid clause might read: “General surface quality per MIL-PRF-13830B, clause 3.5, 80-50; clear aperture zone limited to maximum root area per ISO 10110-7, grade A-A.” That single line keeps ordinary inspection simple while giving the functional area an objective ceiling.
How to write unambiguous procurement clauses referencing MIL-PRF-13830B
Ambiguous drawings are the single biggest cause of rejected optics that technically pass inspection. A clause referencing MIL-PRF-13830B should always state:
- The full specification designation, including revision letter and date.
- The exact clause reference, typically 3.5 for scratch and dig.
- The comparison standard drawing or brand used for the visual check.
- The lighting condition and magnification under which inspection will occur.
- The acceptable scratch-dig pair, for example 80-50, and whether it applies to the whole surface or a defined clear aperture.
- The sampling method: 100% inspection or an agreed sampling plan.
A drawing note might simply state: “Surface quality per MIL-PRF-13830B, clause 3.5, 60-40, inspected against comparison standard drawing C7641866 under diffuse illumination.” When quoting a supplier, ask for a certified comparison set reference, an inspection certificate signed by the operator and batch-level traceability, all of which our optical fabrication guide covers in more detail for teams building their own drawing templates.
Applying the standard in production: Precision Glasses’ approach
Our process integrates MIL-PRF-13830B clause references into RFQ templates and inspection certificates, ensuring customers receive documented pass/fail results against the specified comparison standard and lighting conditions.
Production controls that support this include:
- Inspection checkpoints after coating, cementing and edge finishing, since each process introduces its own characteristic defect types.
- Batch traceability linking finished parts to inspection records, operators, and comparison standards.
- Quality processes that carry through from prototype runs to volume production.
This approach supports traceability of accepted parts back to their inspection conditions, supported by quality testing protocols even long after delivery.
Author perspective: best-practice recommendations from an optics manufacturer
Most disputes over scratch and dig acceptance trace back to a drawing that never named the comparison standard in the first place. Insist on it, every time, along with the lighting and magnification used to judge the part. Where function genuinely depends on sub-visibility imperfections, a dimensional callout beats a comparison grade, however familiar the older method feels. Keep every inspection certificate on file: for defence and aerospace procurement, that record is often the only thing standing between a passed audit and a costly recall.
— Alexandra
How Precision Glasses can help deliver MIL-PRF-13830B compliant parts
Getting from a drawing note to a delivered, inspection-certified part is where most procurement timelines stall. Precision Glasses supports that step directly, from RFQ review through to final acceptance.
Our team can help with:
- RFQ support that clarifies clause references, comparison standards and sampling plans before manufacturing starts.
- Custom optical components, including lenses, windows and cover glass, produced to documented tolerances.
- Inspection certificates and batch traceability records suited to defence, aerospace and medical device procurement.
Browse our optical components catalogue or visit our services page to request a quote for your next MIL-PRF-13830B compliant order.
Sources
- ASSIST-QuickSearch Document Details — MIL-PRF-13830
- The truth about scratch and dig (Savvy inspector series)
- MIL-PRF-13830B optical components fire control — EverySpec
FAQ
What does MIL-PRF-13830B actually specify?
MIL-PRF-13830B is a performance specification covering the manufacture, assembly and inspection of finished optical components such as lenses, prisms and mirrors. Its ASSIST listing confirms current status, revision and any applicable notices.
Does a scratch number mean a specific width in microns?
No. The scratch-and-dig grade is a visibility comparison against a master set, not a direct width measurement, so the same physical defect can grade differently depending on lighting and the comparison hardware used.
When should I use ISO 10110-7 instead of scratch and dig?
Visibility grading suits most conventional optics, but high-resolution or high-brightness systems often need an objective size limit. ISO 10110-7 specifies defects by root area, giving a dimensional ceiling independent of any comparison set.
What should a procurement drawing include to avoid disputes?
A clear drawing states the specification revision, the exact clause (typically 3.5), the acceptable scratch-dig pair, the comparison standard brand or drawing, and the lighting and magnification used for inspection. Precision Glasses builds these elements into RFQ templates and inspection certificates to keep acceptance decisions traceable.
Where can I get the official MIL-PRF-13830B document?
The DLA ASSIST portal is the authoritative source for the current revision and notices. Convenience copies also appear on library sites such as EverySpec, though ASSIST remains the reference for formal status.
