For a standard BSA bottom bracket of 68mm width, in most cases a narrow cone ring (cylindrical width 0.5mm) is appropriate. It's cross section is nearly a triangle. It doesn't add additional width.
If you need additional distance to the frame, you can choose a cone ring, that has an additional cylindrical width of 2, 4 or even 6.5 mm (see photo on the right. Different steel and aluminum cone rings all with milled grooves on the backside).
If you use a nut of more than 2 mm additional width, please also choose the adequate grooved nut on the left side, or you would lose guidance for the left industrial ball bearing.
Same for wider bottom bracket shells: If you have a 70 or 72 mm wide shell, please order a wider nut.
The photo on the right shows three different grooved nuts:
- on the left: the standard nut with a 6 mm wide annular section for the wrench and 45° shape for direct mounting into a chamfered b.b. shell.
- middle and right: grooved nuts with additional 6.5 mm width, used for installation into Bromptons or other extra wide applications. You see one with 90° and one with 45° shape. The 90° version is used for a mountain-drive with torque lever (no reaction torque to be held), the 45° version is used for any drive with conical installation.
A wider cone ring can be necessary for bikes with wide-spread chainstays, as many mountain bikes have.
The outer diameter of all Schlumpf drive housings is approximately 94 mm. This allows you to estimate, if the housing can be mounted directly at the right end of the bottom bracket shell or if it needs an additional width of the cone ring.
Photo at the bottom shows a typical mountain-drive - Brompton setup: the special Brompton torque lever combined with the +6.5 mm grooved nut on the left side, with 45° shape and an aluminum cone ring. The cone ring here is for centering only. Not for holding the reaction torque, as this is done by the torque lever.