HP Velotechnik manufactures their front booms -- those with and without the derailer post -- with threaded bolt holes on both the top and bottom side of the boom. The factory uses the threaded bolt hole on the bottom of the boom for installing the headlight mount for a dynamo headlight. They'll use the threaded bolt hole on top of the boom for installing the odometer mount. Obviously, you could use the bolt holes for installing other accessories.
As for the question about the size of the threaded bolt holes, they are simply the same metric sized bolt holes as those used for bolting on water bottle cages and the cable guides on the Street Machine Gte (and most other mass-market modern bike). Yes, there is an "M" number, but it's easier to remember that it's the same as those used for the water bottle cages.
If you want a headlight, but your SMGte has no derailer mast, there are several ways to solve the problem.
1) Attach a HPV odometer (accessory) mount, suitable for a lightweight headlight, using the threaded bolt hole on top side of boom.
2) Use the strong accessory mount built by Hase (google e.g., "Hase Pino"), which wraps around a front boom and can support a headlight or other accessory.
3) Use the threaded bolt hole accessory mount under the boom with the mounts included with a high end (e.g. B&M) dynamo powered headlight. The Peter White Cycles website has great information about light mounts.
4) Use a nylon Cronometro Nob attached to your front fork or handlebars (see Peter White Cycles website for instructions).
5) Use a high-end helmet-mounted headlight (e.g., from B&M, or Dinotte).
|Hase Accessory Mount|
Stay healthy and stay well-lit,
New York City Recumbent Supply
The Innovation Works, Inc.
copyright 2014 Robert Matson