Silver Plating per QQ-S-365D and ASTM B700
Drawings and purchase orders still call for “silver plated per QQ-S-365D Type I Grade B, .0005 thick”, sometimes written MIL-QQ-S-365 or QQ-S-365. We supply nuts, studs and machined parts silver plated to that callout or to its replacement, ASTM B700, through outside Houston platers, with the plating certified to the specification on the order.
Type I, Grade B, .0005 in.
Types and grades.
If a drawing gives no type, QQ-S-365D accepts Type I, II or III.
A cancelled spec, still on drawings.
QQ-S-365D was cancelled by Notice 1 on 2 February 2001. The notice names ASTM B700, Electrodeposited Coatings of Silver for Engineering Use, as a possible replacement and cautions users to evaluate it for their application before citing it.
The two specs reuse the same words for different things. In QQ-S-365D the Type is the finish and the Grade is the tarnish treatment. In ASTM B700 the Type is purity: Type 1 is 99.9% silver minimum, Type 2 99.0% and Type 3 98.0%. So “Type I” on an old drawing is not the same as “Type 1” on a new one. We plate to whichever the drawing or order names, and any change from one to the other is agreed with the customer first.
What the spec requires of the plater.
- A silver strike goes on before the silver plate. On steel the silver goes over a nickel, or nickel over copper, undercoat.
- Steel parts of Rockwell C40 and harder are baked at 375 ± 25 °F for 3 hours or more, within four hours of plating, for embrittlement relief.
- Steel parts with damaging residual stress from machining, grinding or cold forming get a stress relief at 375 ± 25 °F for 3 hours before plating.
- Thickness on threaded fasteners is measured on the shank or another smooth surface as close to the threads as possible.
- The spec notes that most standard threads do not take much more than 0.00015 in. of coating, so a .0005 in. silver plate needs allowance, usually by tapping the nut oversize.
How to call it out.
- Give the part, its material and the plating line from the drawing, for example ASTM A194 Grade 8M heavy hex nuts, silver plated per QQ-S-365D Type I Grade B, .0005 in. thick.
- Or, to the current spec: silver plated to ASTM B700 Type 1, matte, .0005 in. thick.
- Say whether nuts are to be tapped oversize for the plating, and by how much if your drawing sets it.
- Give the base metal's hardness, so the plater can apply stress and embrittlement relief where the spec calls for it.
- Ask for thickness readings on the certificate if you need them.
Anti-galling on stainless and nickel alloys.
Silver is soft and ductile and acts as a solid lubricant on the thread, so stainless and nickel-alloy nuts run on and come off their studs without galling, including in high-temperature service. See silver plating for how it is applied and where it is the wrong choice, and all coatings and platings for other finishes.
QQ-S-365D silver plating: common questions.
What does “silver plated per QQ-S-365D Type I Grade B .0005 thick” mean?
Electrodeposited silver to Federal Specification QQ-S-365D: Type I is a matte deposit, Grade B means no chromate tarnish-resistant treatment on top, and .0005 in. (0.013 mm) is the silver thickness. That is also the spec's default minimum on functional surfaces when no thickness is given.
Is QQ-S-365D still active?
No. Notice 1, dated 2 February 2001, cancelled QQ-S-365D and named ASTM B700 as a possible replacement, with a caution that users evaluate it for their own application. The old callout is still common on drawings, and platers still work to it.
Is QQ-S-365 Type I the same as ASTM B700 Type 1?
No. The words are reused but mean different things. In QQ-S-365D the Type is the finish (I matte, II semi-bright, III bright) and the Grade is the tarnish treatment. In ASTM B700 the Type is the silver purity (Type 1 is 99.9% minimum). Converting a drawing from one to the other should be agreed with the customer, not assumed.
Will .0005 in. of silver fit on a standard thread?
Usually not without an allowance. QQ-S-365D notes that most threaded parts with standard fits do not take much more than 0.00015 in. of coating, and that heavier plating needs allowance made when the threads are cut. A nut to be plated .0005 in. is normally tapped oversize, by an amount agreed with the plater.
Will Grade B silver tarnish?
It can. Grade B has no tarnish-resistant treatment, and the spec warns that cardboard and paper packing can contain enough sulfur to tarnish silver, so Grade B parts are best packed in sulfur-free or antitarnish material.