Flexible Ureteroscope French Sizes: How Big Is a Ureteroscope?

What French means and how big is a ureteroscope

The French (Fr) scale gives the outer circumference in millimetres; one French equals one third of a millimetre in diameter. An 8.7 Fr shaft is therefore about 2.9 mm across. Ureteroscope sizes quoted in catalogues usually refer to the shaft, but the tip is often smaller and the handle is larger.

So how big is a ureteroscope? Flexible models are long instruments with a very slim insertion portion. The numbers that matter for the ureter are the tip and shaft diameters, and for the tools the working channel diameter. Always compare the same dimension between models.

Tip, shaft and working channel

The tip is the leading part and is made as small as possible so it can enter the ureteric orifice. The shaft is the main section and has to pass through the access sheath. The working channel is the lumen inside, which carries irrigation and instruments; a laser fiber in the channel reduces the flow around it.

The Richard Wolf BOA and COBRA family shows these differences clearly. BOA has an 8.7 Fr shaft and a 6.6 Fr tip and fits access sheaths of 9.5 Fr and above. COBRA has a 5.2 Fr distal tip, a 3.6 Fr working channel and a separate 2.4 Fr laser channel for fibers up to 365 µm.

• Tip diameter: ease of ureteric entry
• Shaft diameter: fit in the access sheath and room for outflow
• Working channel: baskets, forceps and fiber
• Dedicated laser channel: parallel work with a second instrument

Access sheath choice and irrigation

A ureteral access sheath gives repeated access and lowers intrarenal pressure by allowing outflow around the scope. The inner diameter must exceed the scope shaft by enough margin for fluid to leave. If the scope nearly fills the sheath, the outflow is limited and the view and pressure suffer.

Manufacturers state a minimum sheath size for each scope; for BOA it is 9.5 Fr. A thinner scope also allows a smaller sheath, which can ease placement, but sheath use is a clinical decision. See our ureteral access sheath guide for the sheath side.

Instruments and the working channel

Channel size limits what can pass. Nitinol baskets, grasping forceps and laser fibers all need clearance, and a deflected scope narrows the effective path. Use only accessories that the manufacturer lists as compatible, and ask for the maximum accessory diameter in writing. Our guide to graspers and stone baskets covers the options.

Laser fiber size matters too: thin fibers keep deflection and irrigation better, while thicker fibers carry more energy. Choose the fiber and scope together; see the holmium laser fiber guide.

Questions to ask before ordering

Ask for the data sheet of the exact model, with tip, shaft, channel and sheath data. Ask about deflection angle, pediatric suitability, and whether the scope is digital or fiberoptic. Confirm camera compatibility; BOA and COBRA connect to the ENDOCAM Logic 4K controller.

Beckfinity specialists can help match scope sizes to the sheaths, fibers and baskets you already stock. Request a quote through the contact page.