Dental Bur Shanks: FG, RA, HP, and Surgical Length Explained
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The shank is the only part of a bur that has to be right before you start.
Get the shape wrong and you adapt. Get the grit wrong and you reach for another one. Get the shank wrong and the instrument does not seat, or worse, it seats badly and you find out at 200,000 rpm with a patient in the chair.
I run Taft Dental Supply. The single most common pre-purchase question we get is not about grit or shape. It is some version of "will this fit my handpiece." So here is the whole answer: the three shank families, the extended-length variants, how to read the shank off an ISO number, and where the mismatches actually happen.
FG: friction grip, the one in your high-speed
Shank diameter: 1.6 mm. Standard length: 19 mm. ISO shank code: 314.
No latch, no notch, no threads. The shank is a smooth cylinder that slides into the turbine chuck, and the chuck jaws close on it. Friction is the entire retention mechanism, which is where the name comes from.
FG runs in air-driven high-speed turbines and in speed-increasing electric contra-angles. If you are cutting enamel, prepping a crown, or opening access, you are in FG. It is the overwhelming majority of what a restorative practice consumes.
The length variants matter more than most people realize, and they all carry their own ISO code:
- 313, short: better access in the posterior, especially on a patient who cannot open wide.
- 314, standard: 19 mm. The default, and what you should assume unless the box says otherwise.
- 315 and 316, long and extra long: surgical and endodontic reach. More on these below.
One thing worth knowing about friction retention: it depends on the chuck as much as the bur. A worn chuck grips a perfectly good shank badly, and the symptom is vibration and slipping that looks exactly like a bad bur. If a fresh bur from a fresh pack is chattering, suspect the handpiece before you suspect the box.
RA: latch type, the one in your slow-speed
Shank diameter: 2.35 mm. Typical length: 20 to 22 mm. ISO shank code: 204, with 205 for the 26 mm long version.
RA stands for right angle, and these are also sold as CA or latch-type or low-speed burs. The giveaway is physical: there is a notch or flat machined into the back end of the shank. The latch in a slow-speed contra-angle engages that notch and locks the bur mechanically rather than by friction.
RA runs in the 5,000 to 40,000 rpm range. What you want it for is anything where control beats speed: caries excavation with real tactile feedback, finishing, polishing, and endodontic access where you do not want turbine speed near the pulpal floor.
The critical point for ordering: an FG bur will not seat in a latch contra-angle, and an RA bur will not fit a high-speed chuck. The diameters are different and the retention mechanisms are different. This is not a tight-fit situation you can force. It is the most common shank ordering mistake, and it happens because the shapes and the style numbers look identical across both families. A round carbide 4 exists in FG and in RA, and the box art is nearly the same.
HP: straight handpiece, the long one
Shank diameter: 2.35 mm, same as RA. Length: 44.5 mm as standard, 65 mm for the extra-long. ISO shank codes: 104 and 105.
Same diameter as RA, radically different length, and no latch notch. HP burs run in a straight nose-cone handpiece and they are built for work outside the mouth or deep inside it: denture and acrylic trimming, model work, lab adjustment, extraoral finishing, and some oral surgery where the extra reach earns its keep.
Practices that do their own denture adjustments and relines need HP acrylic burs and usually know it. If you do not do lab work chairside, you may never touch this family, and that is fine.
Surgical and extended length: the fourth category
This is not a separate shank family. It is FG that got longer, and it solves a problem shape selection cannot touch.
Standard FG runs 19 to 22 mm overall. In the posterior, and especially on a third molar or a deep surgical site, that is not enough instrument to put the working end where it needs to be without angling the handpiece head into the cheek or your own sightline. A bur you have to tilt to reach with is a bur that will gouge something.
Extended FG runs 25 mm and 28 mm, sold variously as FG L, FG XL, FG SL, or surgical length depending on the manufacturer. Same 1.6 mm shank, same chuck, so it drops into the handpiece you already have.
Where it earns the stock:
- Third molar sectioning, where a Zekrya-type surgical taper is the standard instrument
- Endodontic access refinement with a safe-ended bur, where the inactive tip lets you flare the walls without perforating the pulpal floor
- Crown and root separation
- Deep posterior caries where a standard FG round simply will not seat at the right angle
- Bone removal during surgical access
A warning worth passing on, because it comes up constantly in clinician discussion: extended-length burs break more than standard ones. More overhang from the chuck means more leverage on the shank, and surgical sectioning is exactly where lateral load is highest. Dentists regularly report burning through two or three instruments to section a single upper molar. That is not necessarily a defective bur. It is physics, and the way to plan around it is to have more than one on the tray rather than fighting through with a dulled instrument.
Read the shank straight off the ISO number
Every bur built to ISO 6360 carries a five-segment number, and the second segment is the shank. Once you know that, you never have to guess from packaging again.
The pattern is: material, shank, shape, grit, head diameter.
Take 806 314 166 524 014.
| 806 | Diamond. Carbide uses 500. |
| 314 | FG shank, standard length. This is the segment that decides handpiece fit. |
| 166 | Head shape, a tapered bur with a rounded end. |
| 524 | Grit. Carbides omit this, since blades are not graded by grit. |
| 014 | Head diameter in tenths of a millimetre, so 1.4 mm. |
The shank codes worth memorizing are short:
- 104 and 105: HP, straight handpiece
- 204 and 205: RA, latch type
- 313, 314, 315, 316: FG in short, standard, long, and extra long
The pattern underneath is simple. A leading 1 is HP, a leading 2 is RA, a leading 3 is FG. That one sentence solves most ordering errors.
Two instruments from different manufacturers carrying the same ISO number are the same instrument in shape, grit class, and size. That is the whole point of the standard, and it is why the number is a better cross-reference than the brand style number when you are comparing suppliers.
Four places the wrong shank actually costs you
Reordering by style number alone. A round carbide 4 exists in FG, RA, and HP. Ordering a box of 4s without the shank is how a box arrives that nobody can use. Put the shank in the reorder sheet next to the style.
Assuming your electric handpiece takes RA. A speed-increasing electric contra-angle takes FG, not latch. The head looks like a contra-angle, so the assumption is understandable and wrong.
Buying standard length for surgical work. Not a fit problem, a reach problem. The bur seats fine and then you cannot get the angle, so you compensate with handpiece position and lose your sightline.
Mixing shank families in one cassette. Sorting them apart during reprocessing costs more time than keeping them separate from the start, and a misfiled RA bur in an FG block is a mid-procedure interruption waiting to happen.
What to stock
For a general restorative practice, the honest breakdown is that FG is most of your volume, RA is a small dedicated set, extended FG is a case-by-case stock item, and HP is only relevant if you do lab work chairside.
Standardize your FG shapes first, since that is where the spend concentrates. Our guide to which bur to use for each procedure covers the working set, and the shape and number chart decodes the style codes.
Then add extended length for the surgical and endodontic work you actually do, and keep more than one of each on hand for the reason above.
On what we carry, so you are not guessing: the Taft line is FG. Diamonds and carbides run 19 to 22 mm on a 1.6 mm friction grip shank that fits any standard high-speed handpiece. The surgical and endodontic carbides run extended 25 mm and 28 mm FG shanks, including a safe-ended Endo-Z and a Zekrya surgical taper, six per box. We do not currently stock RA or HP, so if your reorder sheet has latch-type or lab burs on it, those come from elsewhere.
Diamonds are $19.95 for a 5-pack, carbides $29.95 for a 10-pack, everything ships from Cincinnati within 24 hours, and the 60-day guarantee covers opened packs. Browse the catalog, or call 513-580-8414 with a shank question before you order rather than after.
Common questions
What is the difference between FG and RA dental burs?
FG stands for friction grip. The shank is 1.6 mm in diameter with a smooth end, and it is held in a high-speed handpiece by the friction of the chuck jaws. RA stands for right angle, also called latch type. The shank is 2.35 mm with a notch machined into the end that a slow-speed contra-angle latch locks onto. They are not interchangeable in either direction: the diameters differ and so do the retention mechanisms.
What does HP mean on a dental bur?
HP means handpiece, referring to a straight nose-cone slow-speed handpiece. HP burs share the 2.35 mm shank diameter of RA burs but are much longer, typically 44.5 mm, and have no latch notch. They are used for denture and acrylic trimming, model and lab work, extraoral finishing, and some surgical applications.
How long is a surgical length dental bur?
Extended FG burs generally run 25 mm or 28 mm overall, against 19 to 22 mm for standard FG. They are sold as FG L, FG XL, FG SL, or surgical length depending on manufacturer. The shank diameter stays 1.6 mm, so they fit the same high-speed handpiece. The extra reach makes them standard for third molar sectioning, deep posterior access, and endodontic work.
How do you tell what shank a bur has from the ISO number?
The second group of three digits in a five-segment ISO 6360 number is the shank code. A leading 1 means HP, a leading 2 means RA, and a leading 3 means FG. So 314 is a standard FG shank, 204 is latch type, and 104 is straight handpiece. The specific codes also encode length: 313 is short FG, 314 standard, 315 long, 316 extra long.
Why do surgical length burs break more often?
More shank extends beyond the chuck, which increases the leverage applied to it under lateral load. Surgical sectioning is exactly the application where lateral load is highest, so the combination is unfavourable. Clinicians commonly report using more than one instrument to section a single molar. Planning for that is more practical than pushing a dulled or stressed bur through the rest of the case.
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