Never seen one of these before, anyone know what’s its function ?
RORY
A drone stop?
Here’s the original post:
https://www.facebook.com/photo.php?fbid=211586555940194&set=gm.10155268931488238&type=3&theater
The caption seems pretty clear to me 
Oh right, I came across the photo somewhere else. Great way to achieve single drone stopping . I thought it might be a way to alter the pitch for the drone. Dave williams made drones with an extra outlet hole which changed the pitch of the drone to another key.
RORY
Dave williams made drones with an extra outlet hole which changed the pitch of the drone to another key.
I believe Matt Kiernan did that originally. I seem to remember Tommy Keane playing a Matt Kiernan half set during the early eighties that was set up to play in both D and C.
I cannot identify it to species, but it does appear to be ovipositing in that drone.
Much like this brown hawker.
Why, so it does! 
A standard Northumbrian trick (as I’m sure you know). The 17 key (count 'em!) set I had in my possession briefly before I realised I am not a mechanical genius had drones that could play three different pitches. There’s a fine line between genius and insanity…
Then, it’s not a drone stop, per se, but a drone extender? If it changes the pitch from D to C, I imagine that this mechanism is hollow and is used to lengthen the drone to which it’s attached? So, when open it plays D and when closed it plays C? Is there a stop function to it as well?
Then, it’s not a drone stop, per se, but a drone extender?
We’re talking about two different things. The photo Rory posted shows a drone stop.
I thought it might be a way to alter the pitch for the drone. Dave williams made drones with an extra outlet hole which changed the pitch of the drone to another key.
Is about something else, a hole in the side of a drone that can be covered by a moving ferule in order to change the pitch of the drone (eg, shorten a C drone to D).
On Northumbrian pipes the rings to change the drone pitch are called “tuning beads” though the person describing it as a movable ferrule with a hole is closer to what it is. Northumbrian pipes also have drone end stoppers though they operate differently to the one shown at the start of this thread. The tone hole at the end of the drone is on the side and end is capped with a small piston going through the cap. This can be pushed in so that it seals off the hole.
Most Northumbrian sets have four drones, though only three are used at a time. For a basic standard set nominally in G (which could really be F or F#) the drones would be g,d,G,D, with a tuning bead on the G drone allowing it to sound A. This allows drones to be tunes to gdG if playing in G and dAD if playing in D.
My own 17 keyed set has two tuning beads on each drone allowing :-
G with gdG
D with dAD or adD
A with aeA
e minor with eBE
and other combinations yet to be explored…
Ian
The Dave williams Drone with tuning ring thing
RORY