Written and maintained by CASRAI Editorial Board
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General product and regulatory information only, not medical advice. It does not describe how any device is used on a patient.
Short answer
A urethral dilator is a slender hollow or solid instrument, made of metal, plastic or another suitable material, that is used to dilate the urethra. In US regulation the term is also the heading for a family of devices: 21 CFR 876.5520 groups mechanical urethral dilators, urological bougies, metal or plastic urethral sounds, urethrometers, filiforms and filiform followers together, and the FDA classifies them differently (Class I or Class II).
Definition and scope
The FDA’s regulation for this device, 21 CFR 876.5520 “Urethral dilator”, identifies it as a device that consists of “a slender hollow or solid instrument made of metal, plastic, or other suitable material in a cylindrical form and in a range of sizes and flexibilities,” and states that it “is used to dilate the urethra.” The same paragraph states that the generic type “includes the mechanical urethral dilator, urological bougies, metal or plastic urethral sound, urethrometer, filiform, and filiform follower.” So in regulatory language a “dilator”, a “bougie” and a “sound” are not three unrelated products; they are named members of one device type.
The FDA’s review panel for the type is Gastroenterology/Urology. The FDA classification record for the generic “Dilator, urethral” (product code KOE) lists it as not implanted and not life-sustaining.
How the devices are described
The regulation describes the instruments by form and material: slender, hollow or solid, cylindrical, metal or plastic, and made in a range of sizes and flexibilities. It does not set lengths, diameters or curvature, and the text does not publish a size chart. Any size designation printed on a product comes from the manufacturer’s labeling, so a size reference should be taken from the item’s own packaging or instructions for use, not from the regulation.
Types of urethral dilators and sounds
The regulation and the FDA product classification database separate the family into six named types. Searchers often meet them as “types of urethral dilators” or “urethral dilator types”; this table follows the regulation’s own list.
| Device type (21 CFR 876.5520) | FDA product code | FDA class | Premarket notification (510(k)) |
|---|---|---|---|
| Mechanical urethral dilator | FAH | II | Not exempt (the regulation names mechanical dilators as the exception) |
| Urethral dilator (generic record) | KOE | II | Exempt, subject to the limitations in 21 CFR 876.9 |
| Metal or plastic urethral sound | FBX | I | Exempt, subject to the limitations in 21 CFR 876.9 |
| Urological bougie | FAX | I | Exempt, subject to the limitations in 21 CFR 876.9 |
| Urethrometer | FBR | I | Exempt, subject to the limitations in 21 CFR 876.9 |
| Filiform and filiform follower | FBW | I | Exempt, subject to the limitations in 21 CFR 876.9 |
The regulation text reads: urethral dilators in general are Class II (special controls) and exempt from premarket notification, “Except when it is a mechanical urethral dilator”; the urethrometer, urological bougie, filiform and filiform follower, and metal or plastic urethral sound are Class I and exempt from premarket notification, subject to the limitations in 21 CFR 876.9.
Urethral sound sizes
Sound sizes are not set by the regulation or by the FDA classification records, which list no French, gauge, length or curvature values. The class of a sound (Class I) does not depend on its size in these records.
Where it matters for labs, clinics and supply decisions
For a clinic or a supply record, the useful point is that the family does not share one regulatory status. Of the six types above, the metal or plastic sound, the bougie, the urethrometer and the filiform set are Class I, while the generic dilator and the mechanical dilator are Class II, and the mechanical dilator is the only one the regulation excludes from the premarket notification exemption. A catalogue line that says only “urethral dilator” therefore does not tell you which product code and class apply.
A record-keeping checklist
- Write the item name exactly as the label or instructions for use give it (dilator, sound, bougie, filiform, urethrometer).
- Match that name to the type in 21 CFR 876.5520 and note the FDA product code (FAH, KOE, FBX, FAX, FBR or FBW).
- Record the class shown in the FDA product classification database and the date you checked it; the database is updated over time.
- Record the material named on the label (metal, plastic) and whether the label says single-use or reusable, as the manufacturer states it.
- Keep the manufacturer’s instructions for use with the item record.
For related supply-record topics see the urology clinic supply checklist, the guide to catheter balloon sizes, the cystoscopy drape guide, and how the FDA classes kits in surgical packs.
Common misunderstandings
- “Dilator”, “sound” and “bougie” are one thing. They are related names within one regulation, but the regulation lists them as separate types with their own product codes.
- All urethral dilators are the same class. Per the regulation, the sound, bougie, urethrometer and filiform are Class I; the generic and mechanical dilators are Class II.
- Exempt means unregulated. An exemption from premarket notification is limited by 21 CFR 876.9, and the FDA record for the sound (FBX) still lists a Class 1 device with a regulation number.
- The regulation tells you the size. It does not; sizes are set by the manufacturer’s labeling.
FAQ
What is a urethral dilator?
A slender hollow or solid instrument of metal, plastic or other suitable material that is used to dilate the urethra, as defined in 21 CFR 876.5520.
What are the types of urethral dilators?
The regulation names mechanical urethral dilators, urological bougies, metal or plastic urethral sounds, urethrometers, filiforms and filiform followers.
Is a urethral sound a urethral dilator?
A metal or plastic urethral sound is one of the named members of the urethral dilator device type in 21 CFR 876.5520, with its own FDA product code (FBX) and Class I status.
What are urethral sound sizes?
The regulation says only that these instruments come in a range of sizes and flexibilities; neither it nor the FDA classification records specify sizes. Sizes are given in each manufacturer’s labeling.
What FDA class is a urethral dilator?
Class II for urethral dilators in general, including the mechanical dilator; Class I for the sound, bougie, urethrometer, filiform and filiform follower.
Sources
- eCFR, 21 CFR 876.5520 Urethral dilator, checked 2026-10-31.
- FDA Product Classification Database, product code KOE, Dilator, urethral, checked 2026-10-31.
- FDA Product Classification Database, product code FBX, Sound, urethral, metal or plastic, checked 2026-10-31.
- FDA openFDA device classification API, records for regulation 876.5520 (FAH, FAX, FBR, FBW, FBX, KOE), checked 2026-10-31.
