The Madera Helm Spline Drive Sprocket is a black bicycle chainring made from 7075 aluminum with a splined steel insert, featuring 20 teeth in a symmetrical design, elegantly displayed against a plain white background.

A Madera Helm Spline Drive Sprocket made of 7075 Aluminum on a white background.

Description

The Madera Helm is a spline drive sprocket machined from 7075 aluminium in the USA. Instead of a sprocket bolt it uses a hardened chromoly steel insert that matches the 48 splines on the bottom bracket axle, so drive goes straight from the spindle to the sprocket.

It is made for 19mm 48 splined Profile spindles and is supplied with the splined steel insert. Sizes are 25t and 28t with 1/8" tooth width, and the 25t weighs 81g. Spline drive sprockets are not compatible with right side drive two piece cranks because there is not enough room for the splines, though they do work on left side drive two piece cranks.

Features

No sprocket bolt needed. A hardened chromoly steel insert engages the 48 splines on the spindle, so drive is direct and there is no sprocket bolt in the setup.
Fits 19mm 48 spline Profile spindles. Madera list it for 19mm 48 splined Profile spindles, and it may not fit other 19mm 48 splined cranks, so check yours first.
7075 aluminium, made in USA. The sprocket body is machined from 7075 aluminium in the USA, with the steel insert taking the drive load.
25t or 28t sizes. Two tooth counts with 1/8" tooth width, and the 25t comes in at 81g.
Not for RHD two piece cranks. There is not enough room for the splines on right side drive two piece cranks, though left side drive two piece cranks are fine.

Specifications

Spindle: 19mm 48 splined Profile spindles
Teeth: 25t or 28t
Chain size: 1/8" tooth width
Material: 7075 aluminium with hardened CrMo steel insert
Included: Splined steel insert
Weight: 81g (25t)
Note: Not compatible with 2 piece cranks for right side drive, as there is not enough room for the splines. Compatible with left side drive 2 piece cranks. May not be compatible with other 19mm 48 splined cranks.