Guide
Straight vs diamond knurling: which pattern, which pitch, and how do you call it out on a drawing?
Knurling is a turning operation that presses (or, less often, cuts) a row of small V-shaped teeth into a cylindrical surface, either as straight ridges parallel to the axis or as a crossed diamond pattern. A straight knurl mostly locks a part against rotation or grips a mating bore; a diamond knurl mostly gives a hand grip. The pitch, the blank diameter and the tolerance class decide whether the pattern comes out clean.
By Saola Manufacturing engineering team · Published · Updated
A note such as “DIAMOND KNURL, MEDIUM” is enough for a decorative grip, but not for a knurl that has to press into a housing. This guide covers the pattern choice, the diametral pitch system of ASME B94.6, and callouts an overseas supplier can quote without questions. Figures describe the published standard, not any shop’s capability.
On this page
What is the difference between a straight knurl and a diamond knurl?
A straight knurl has teeth that run parallel to the part axis, so it resists rotation and slides into a mating bore along its length. A diamond knurl crosses a right-hand and a left-hand helix, which leaves a field of small pyramids that resist slip in every direction and feel good under the fingers.
ASME B94.6 covers three patterns on cylindrical surfaces: straight, diagonal and diamond (ASME, B94.6 Knurling). A diagonal knurl is a single helix, right-hand or left-hand. A diamond is two diagonals crossed, and it comes in two forms that are easy to confuse on a drawing:
- Raised-point (male) diamond on the part. The part ends up covered in pointed pyramids. This is the familiar grip pattern on thumbscrews and knobs. It is made either with a pair of diagonal knurls of opposite hand or with a single knurl that carries a depressed-point pattern.
- Depressed-point (female) diamond on the part. The part ends up with small pockets and a flatter feel. It needs a single knurl with raised points, and it is much less common.
Because a tool that forms raised points leaves pockets in the part, the note should always describe the result on the part, not the tool. “Diamond, raised points” removes the ambiguity. A tool maker’s technical guide also notes that diamond knurls need more forming pressure than straight or diagonal ones, which matters on long, thin parts that can deflect under the tool (Reed Machinery, Knurls & Knurling technical data).
When should a drawing call for straight knurling instead of diamond?
Call for straight knurling when the knurl has a mechanical job: locking a pin, shaft or insert into a softer mating part, transmitting torque through a press fit, or holding a close outside diameter. Call for diamond knurling when the job is a hand grip or appearance and the outside diameter only needs a loose tolerance.
The reason is geometric. Straight teeth enter a bore along their own length, so each tooth cuts or displaces a matching groove in the hub and the joint carries torque through that interlock. German practice uses the same logic: knurled press joints on cylindrical parts are mostly made with axially parallel teeth, the RAA form of DIN 82 (Wikipedia (de), Rändelung). A diamond forced into a bore tends to tear the hub rather than groove it cleanly.
Diamond knurls win where people touch the part: thumbscrews, knobs, handles and caps, because the pattern grips whether the hand twists or pulls.
A quick test: a knurl that mates with another part or carries a tight diameter tolerance should be straight.
What are the standard knurl pitches under ASME B94.6?
ASME B94.6 standardizes four diametral pitches for knurls: 64, 96, 128 and 160. Per ASME B94.6, diametral pitch is the number of teeth on the work divided by the work blank diameter in inches, so a 96 pitch knurl puts 96 teeth around every inch of blank diameter.
| Diametral pitch | Circular pitch (in) | Approx. teeth per inch | Blank diameter steps | Approx. OD increase, straight (in) | Approx. OD increase, diagonal (in) |
|---|---|---|---|---|---|
| 64 (avoid if possible) | 0.0491 | 20.4 | 1/64 in | 0.024 | 0.021 |
| 96 (preferred) | 0.0327 | 30.6 | 1/32 in | 0.016 | 0.014 |
| 128 | 0.0245 | 40.7 | 1/64 in | 0.012 | 0.010 |
| 160 | 0.0196 | 50.9 | 1/32 in | 0.009 | 0.008 |
Two columns in the table do the real work. The circular pitch is simply pi divided by the diametral pitch, the tooth spacing measured around the circumference. The blank diameter steps show why the system exists: per ASME B94.6, the 96 and 160 pitches divide evenly into blanks in 1/32 in steps, and the 64 and 128 pitches into blanks in 1/64 in steps. Ordinary fractional bar and turned sizes therefore take a whole number of teeth without any fiddling.
The standard asks designers to avoid the coarse 64 pitch where they can and to prefer 96, so that fewer knurl sizes are needed across a plant. The technical data also says the standard applies to work diameters up to 1 in and lists a minimum tooth count for each pitch. Above that size, or on a metric blank, the same formula still predicts tracking, but the tables stop.
Older drawings use the circular pitch system and give teeth per inch. The same tool maker notes that coarse, medium and fine were used loosely across a wide range of tooth spacings, and recommends stating the actual teeth per inch: “medium” on a drawing is a question, not a specification.
Why does the blank diameter decide whether a knurl comes out clean?
A knurl forms a clean pattern only when the blank circumference holds a whole number of teeth, so the knurl lands in its own grooves on every revolution. If the diameter holds a fraction of a tooth, the knurl double-tracks and leaves a shallow, torn or doubled pattern.
Per ASME B94.6 the tooth count on the work is the diametral pitch times the blank diameter. A 0.375 in blank with a 96 pitch knurl gives exactly 36 teeth, per ASME B94.6, and tracks cleanly. Move that blank to 0.380 in and the count becomes 36.48 teeth, which the knurl cannot resolve. That is why the knurled diameter on a drawing should come from the standard’s tables or the formula, not from a round number chosen for the look of the dimension.
Diagonal and diamond knurls produced by end-feeding with straight knurls tilted to a helix angle follow a modified formula. Per ASME B94.6 the teeth are counted in the transverse plane, so the tooth count becomes the pitch times the diameter times the cosine of the helix angle, and the theoretical blanks are decimal sizes rather than fractions. This is one more reason to state the helix angle on a diamond callout.
The blank itself needs a tolerance tight enough to keep the tooth count whole. Per ASME B94.6 the recommended blank tolerance is tied to the circular pitch, about 6% of it for Classes I and II and 3% for Class III, which on a 96 pitch blank is a total band of about 0.002 in for the first two classes and half that for Class III. Holding a blank to that band is ordinary turning work; on a Saola CNC turning order, the blank tolerance is reviewed with the other turned dimensions and confirmed in the quote.
How much does knurling grow the diameter, and what are knurl tolerance classes?
Formed knurling pushes material up as well as down, so the knurled diameter ends up larger than the blank, by roughly half the tooth depth on each side. ASME B94.6 sets three tolerance classes for that knurled diameter, from Class I for grip and appearance to Class III for knurls used as close fits.
| Class | Patterns allowed | Typical use | Knurled OD tolerance, 96 DP (in) |
|---|---|---|---|
| I | Straight, diagonal, raised diamond | Grip, decoration, inserts for moldings and castings | +0.004 / −0.010 |
| II | Straight only | Closer control of the knurled OD | +0.000 / −0.009 |
| III | Straight only | Closest control, knurls used for close fits | +0.000 / −0.005 |
Two points follow from the table. First, a diamond knurl can only be Class I under the standard. If the drawing puts a tight tolerance on a diamond-knurled diameter, the note and the pattern are in conflict, and the supplier will ask which one wins. Second, only straight knurls can be Class II or III, which lines up with their use in press fits: the knurl is the interference, so its diameter is a functional dimension.
For a press-fit knurl, design the hub bore from the knurled diameter, not the blank, and confirm the fit with a sample assembly, because the result depends on the hub material as much as on the knurl.
Cut knurling removes material instead of displacing it, so it grows the diameter little and loads the part far less, which suits thin-walled parts. Formed is the default assumption, so write “CUT” if you need it.
How do you write a knurl callout on a drawing?
A complete knurl callout gives the pattern, the pitch with its system, the tolerance class, the knurled length, and either the blank diameter or the knurled diameter with the other marked as reference. For diagonal and diamond knurls, add the hand or the point form and the helix angle.
Three illustrative examples, with numbers taken from the tables of the standard:
- Press-fit pin, straight knurl. “STRAIGHT KNURL, 96 DP, CLASS III PER ASME B94.6. KNURLED Ø.391 +.000/−.005. BLANK Ø.375 REF. KNURL LENGTH .25.” Class III is a tolerance on the knurled diameter, so that is the toleranced size, taken from the 96 DP row of the table above, and the blank is marked as reference. Per ASME B94.6 the .375 blank takes 36 teeth at 96 pitch and knurls to about .391.
- Thumbscrew head, diamond knurl. “DIAMOND KNURL, IN-FEED, RAISED POINTS, 30° HELIX, 96 DP, CLASS I PER ASME B94.6. BLANK Ø.500. KNURL LENGTH .31.” Class I is the only class available to a diamond, and a grip rarely needs more. The fractional .500 blank suits an in-feed diamond rolled with a pair of diagonal knurls; an end-fed diamond needs one of the standard’s decimal blanks instead.
- Metric drawing. “KNURL RGE 0.8 DIN 82” for a raised-point diamond with a 0.8 mm pitch, per DIN 82 designations; the full form letters are listed in the next section.
Show whether the knurl runs into a shoulder or stops short of it, since an end-fed knurl cannot reach a shoulder. And say what the knurl is for: “press into ADC12 casting” or “hand grip” beside the note lets the supplier match tooling and inspection to the job.
How are knurls designated on metric drawings under DIN 82?
DIN 82 names each knurl form with a three-letter code and gives the pitch in millimeters. RAA is the straight knurl with axially parallel teeth, RBL and RBR are left-hand and right-hand diagonals, and RGE is the raised-point diamond, the most common grip pattern.
- RAA: straight knurl, teeth parallel to the axis.
- RBL / RBR: left-hand or right-hand diagonal knurl.
- RGE / RGV: diamond formed from left- and right-hand teeth, with raised (E) or depressed (V) points.
- RKE / RKV: cross knurl, with raised (E) or depressed (V) points.
The German-language reference on the process gives these letters and notes a standard profile angle of 90°, with a wider angle in special cases (Wikipedia (de), Rändeln). ISO 13444 turns up in a different context: the companion article on knurled press joints refers to a press-fit knurl “type A per ISO 13444” (Wikipedia (de), Rändelung), so if a metric drawing cites that number, confirm which knurl type is meant. A metric designation fixes the pitch but not a tolerance class in the ASME sense, so a DIN 82 callout on a functional knurl still needs the knurled diameter and its tolerance written out.
What should you send an overseas supplier with a knurled part?
Send a drawing that names the knurl system, pattern, pitch and class, with the knurled diameter and length toleranced, plus a note on the function of the knurl. A shop in Vietnam, Mexico or anywhere else can then pick matching tools and quote the part as drawn.
- Name the system. Knurl tooling is sold in diametral pitch, in teeth per inch and in metric pitch. Stating “96 DP per ASME B94.6” or “DIN 82” tells the supplier which tool family to buy or pull from stock.
- Ask for the tool to be confirmed in the quote. If the supplier proposes a near equivalent, such as a metric pitch in place of a diametral pitch, that should show up before the first article, not after.
- Agree on inspection. Knurled diameters are measured over the crests. Say whether a micrometer reading, a ring gauge or a trial assembly into the mating part is the acceptance test.
- Flag finish interactions. Plating or anodizing after knurling adds a layer on the crests and can dull sharp points; note whether the knurled diameter applies before or after finishing.
The RFQ package guide lists the rest of what to send with the drawing. When the package is ready, send it for a quote; any knurl note that needs clarification is raised in the reply, before tooling is chosen.
Frequently asked
Is a diamond knurl stronger than a straight knurl in a press fit?
Usually not. Straight teeth enter the hub along their length and cut or form matching grooves, which is why press-fit knurls are almost always straight. A diamond tends to tear the hub material and gives a less predictable joint.
What does “medium knurl” mean?
Nothing precise. Coarse, medium and fine have been used for a wide range of tooth spacings. Replace the word with a diametral pitch, a teeth-per-inch value or a DIN 82 pitch.
Can I put a tight tolerance on a diamond-knurled diameter?
Under ASME B94.6, raised diamond knurling falls only in Class I, the loosest class. If a diameter must be held closely, make that feature a straight knurl or a plain turned diameter.
Should the drawing give the blank diameter or the knurled diameter?
Give the one that matters functionally and mark the other as reference. For a grip, the blank is usually enough. For a press fit, tolerance the knurled diameter and let the supplier set the blank that produces it.
Sources
- ASME B94.6, Knurling, ASME, 1984 edition (listed as current, S2025), scope page accessed September 2026
- Knurls & Knurling, technical data, Reed Machinery, Inc., reproducing ANSI/ASME B94.6-1984 tables; archived copy accessed September 2026
- Rändeln (DIN 82 knurl forms), Wikipedia (German), revision of June 2025, accessed September 2026
- Rändelung (knurled press joints), Wikipedia (German), accessed September 2026