A shout-out to Bike Box. A helpful German bike shop.

This looks to me like the arm of a Burley trailer,
attached to a mountain bike via Weber's hitch.

A shout-out to Bike Box, in Frittlingen, Germany for their help.  I'm trying to get a Weber hitch for a customer with a Scorpion fs 26 and a Burley Child Trailer.  They're being immensely helpful.  Burley doesn't (yet) sell this part in the USA.

The situation:
To attach a trailer to an HP Velotechnik trike, you need to use a special mounting bracket for the trike.  It is made by HP Velo.  From there, you need the hitch made by Weber.  (Weber also makes trailers, by the way.)  There are two parts to the Weber hitch: the bicycle (male) end, which attaches to the mounting bracket on the trike/bike, and the trailer (female) end, which attaches to the trailer arm.  HP Velotechnik makes the bracket and sells it with the bicycle (male) end.  For the end that attaches to the trailer arm, we're dependent on the trailer company (Burley).

As I write, Bike Box is helping us figure out which part, exactly, we need.  And you too can reap the benefit through the info. here.  In the future, maybe we can convince Burley USA to carry the part.  Maybe?

The part on the right attaches to the trailer.

You need the 23.5 mm version of this.

Here is the part (for as long as this link works):
"Weber Deichselanschluss ohne Kupplung für Kinderanhänger"
and "Umrüstset, 23.5 4-Kant für Burley"
Their article number is: 510
https://www.bikebox-shop.de/kinderanhaenger-fahrradanhaenger/croozer-kinderanhaenger-fahrradanhaeger/weber-deichselanschluss-ohne-kupplung-fuer-kinderanhaenger/a-510/

Under the product, where you see the text "Auswahl," this is a drop-down list box.  Click it to select the correct size.

- If the arm of the trailer is square, as for the Burley, you need a 23.5 changing set (Umrüstset)
Select: "23.5 4-Kant für Burley"

- If the arm is round you need a 27.5 (Umrüstset)

When you use the site, if you don't speak German, use Google's translate feature and it'll all make more sense.


Have fun and stay well,
Robert
------------
Robert Matson
New York City Recumbent Supply
The Innovation Works, Inc.
copyright 2013 Robert Matson