FG vs. RA Shanks Explained: Choosing the Right Bur Shank for High-Speed and Slow-Speed Handpieces

Published by Deutsche Dental Technologien

Every dental bur has two ends: the working end that gets all the attention, and the shank that determines whether the instrument will fit your handpiece at all. Order the right shape in the wrong shank and the bur is useless chairside — which is why "FG or RA?" is the first question to settle before any bur purchase, and why Busch encodes the answer permanently into every instrument's ISO number.

This guide explains the difference between FG and RA shanks, the speed and torque logic behind each, the long and extra-long variants Busch produces, the lab-side HP shank, and how to read the shank code on any instrument in the Busch rotary range before you order.

The Two Clinical Shanks at a Glance

FG (Friction Grip) is the slender 1.6 mm smooth shank held by a friction chuck in high-speed handpieces and electric attachments. There is no latch and no notch — the chuck grips the shank by pressure alone, which is exactly what allows the instrument to run true at very high rotational speeds. FG is the shank of high-speed dentistry: cutting enamel, preparing cavities and crowns, sectioning restorations.

RA (Right Angle / latch-type) is the thicker 2.35 mm shank with a flat and a latch groove at the end, designed for slow-speed contra-angle handpieces. The mechanical latch positively locks the instrument, which suits the higher torque and lower speeds of contra-angle work: caries excavation, finishing, polishing, and prophylaxis. In Busch catalog notation you'll see these listed as W/RA/CA — the same 2.35 mm latch shank under its German (Winkelstück), US (RA), and contra-angle (CA) names.

Why Speed Dictates the Shank

The division is not arbitrary — it follows physics. At the 150,000–400,000+ rpm of an air turbine, any imbalance is amplified enormously; the FG friction chuck grips the shank concentrically along its length, keeping runout minimal where it matters most. Busch's speed recommendations tell the story: standard FG preparation carbides like the 21-series run at up to 225,000 rpm, and premium FG diamonds carry shape-specific maximums (many long instruments are capped at 110,000–150,000 rpm to control tip whip).

RA instruments live at the other end of the scale. Busch's 1SX and 1SXM excavating burs — supplied in W/RA/CA — are specified at just 500–3,000 rpm depending on head size, where the latch handles torque and the operator retains the tactile feedback that careful caries removal demands. LongLife PERIO-PRO and Dia PERIO-PRO root-surface instruments run RA at 8,000–12,000 rpm. Polishers, prophy cups and brushes, and adhesive-removal instruments like the 9650-series RA polishers are RA by design: low speed, high control, minimal heat.

The practical rule: if the step removes hard tissue fast, it's FG; if the step demands torque, control, or gentleness, it's RA. Most restorative procedures use both in sequence — FG diamonds and carbides for the preparation, RA instruments for excavation, finishing, and polishing. Always pair the shank with the manufacturer's speed specification; Busch publishes these per instrument in the sterilization and speeds library.

Long and Extra-Long Variants

Both shank families come in extended lengths for reach into deep preparations, surgical sites, and posterior access:

• FG lg and FG x-lg — long and extra-long friction grip. Busch uses these for deep-reach instruments like the 700XXL crown-length fissure burs, surgical FG x-lg bone cutters, and the long-neck ZIRAMANT zirconia instruments.
• W-lg/RA-lg/CA-lg and x-lg — extended latch shanks, common on surgical and excavating instruments where working depth exceeds a standard shank.

Related but distinct: Busch's slender-neck designs (like the 1SXM) keep a standard shank but thin the neck between shank and head, improving sightlines into minimal-access excavations without changing handpiece compatibility.

The Third Shank: HP for the Laboratory

Lab-side instruments use the HP (handpiece) shank — a 2.35 mm shank like RA but longer and without the latch groove, held in the collet of a straight laboratory handpiece. Busch lists these as H/HP/PM. You'll find HP shanks throughout the laboratory rotary range: prosthesis carbides, lab diamonds, DiaTWISTER acrylic instruments, and the 141-series surgical bone cutters that run in surgical straight handpieces. If a bur is destined for a benchtop micromotor rather than a patient's mouth, it's almost certainly HP.

Reading the Shank From the ISO Number

The second three-digit block of every ISO number identifies the shank and length — useful when a listing photo is ambiguous:

• 104 — HP (straight handpiece)
• 204 — RA/CA latch, standard length
• 205 / 206 — RA long / extra-long
• 314 — FG, standard length
• 315 / 316 — FG long / extra-long

So ISO 500 314 001… is an FG carbide, ISO 500 204 001… is the same head on an RA shank, and ISO 806 316… is an extra-long FG diamond. Many Busch shapes — the 1-series rounds, 801 diamonds, 44E finishers — are manufactured in multiple shank versions with identical working ends, so a practice can run the same geometry at high speed and in the contra-angle. For the full six-block breakdown, see our ISO numbering guide.

Choosing and Ordering: Practical Guidance

• Match the shank to the step, not just the shape. A 7-series pear exists because cavity outline form needs it; whether you buy it FG depends on whether you cut that outline at high speed.
• Never force a mismatch. An RA shank will not seat in a friction chuck, and running any instrument above its rated speed risks shank slip, runout, and instrument fracture.
• Check the latch. RA instruments assume a standard latch contra-angle; surgical and implant handpieces may use locking systems — confirm compatibility for 2.35 mm surgical instruments such as trephines.
• Filter by shank when browsing. Collections like Cavity Preparation can be filtered by FG and RA tags, so you can build the high-speed and slow-speed halves of a procedure tray separately.
• Store by sequence. Keeping FG and RA instruments in designated positions in STERI-SAFE bur blocks prevents chairside mix-ups and speeds setup.

Conclusion

FG and RA are not competing standards — they are two halves of one workflow. The friction-grip shank exists so diamonds and carbides can run true at the speeds enamel demands; the latch shank exists so excavators, finishers, and polishers can deliver torque and tactility at speeds tissue tolerates. Busch manufactures both (plus the lab-side HP) across its shape range with the shank coded into every ISO number, so the right version is always identifiable before you order.

Browse carbides, diamonds, and polishers by shank at Deutsche Dental Technologien, or contact our team if you're unsure which shank version of a Busch shape matches your handpiece setup — the full specification tables are also in the Busch catalog library.

Related resources: Bur Comparison Chart · Speed Chart · Bur Glossary