I believe a $13 Gitzo thumb screw with wheel will work until you can locate the real deal. The genuine Linhof part is actually very nice (thick, heavy duty, good in the hand) and worth the price. Alternatively you could talk to a machinist or rummage a parts bin. You can definitely find the Gitzo screws at any good camera supply.
Traditionally, tripod threads were 1/4" 20 tpi British Standard Whitworth which is very similar to 1/4" UNC, bot not identical (five degree difference in cut angle).
Today you are likely to find both in use. It would make sense to find out which thread your camera has, particularly if it's a heavy camera.
It is several inches long, has a machined shaft, brass and looks nothing like anything found at Home Depot or Lowes.
I have thread gauges in both 60° UNC and 55° Whitworth, and several tripods, so I'll measure the screws.
Since Whitworth threads fell out of favor before WWII, I'm inclined to doubt your statement, but I can't say it's wrong.
I'll report back.
Also, the 003663 has a 3/8" retaining thread to keep the 1/4" or the 3/8" bolt from falling out accidently from the head. While some Gitzo bolts also have the 3/8" retaining or keeper thread it is spaced differently then Linhof's.
It does not take very long to get the proper screw from the factory but at this time we don't have any left in stock.
From Wikipedia (I know it's not the holy grail of information):
Nearly all current stills cameras accept a 1/4 in Whitworth tripod thread in their baseplate and many motion picture cameras accept a 3/8 in Whitworth, while a 5/8 in thread is the accepted standard for tripod mounted land surveying equipment.
The Leica Thread-Mount used on rangefinder cameras and on many enlarging lenses is 39 mm by 26 turns-per-inch Whitworth, an artifact of its having been developed by a German company specializing in microscopes and thus equipped with tooling capable of handling threads in inches and in Whitworth.
If Whitworth was being used by German camera manufacturers then it pre-dates the existence of UNC. The last time I looked into this, I found one tripod manufacturer specifying Whitworth and one specifying UNC but I see no reason to doubt that originally it was Whitworth.
And this from a Wiki page on tripod threads:
I don't agree with the last line! It's more likely that modern tripod manufacturers are using a 1/4" 20 tpi thread with a cut profile designed to fit either thread without binding.Screw thread
Per ISO 1222:2010, the current tripod screw thread standard for attaching the camera calls for a 1/4-20 UNC or 3/8-16 UNC thread. Most consumer cameras are fitted with 1/4-20 UNC threads. Larger, professional cameras and lenses may be fitted with 3/8-16 UNC threads, plus a removable 1/4-20 UNC adapter, allowing them to be mounted on a tripod using either standard.
Historically, the thread standard for attaching older cameras to tripods was 1/4-20 BSW for smaller cameras or 3/8-16 BSW for larger cameras and pan/tilt heads. In this application the BSW and UNC thread profiles are similar enough that one can mount a modern camera on a legacy tripod and vice versa.
Oh I am not debating whether or not the OEM Linhof part is worth it - it is. Just that in a pinch he might make it work.
When Ford bought Jaguar...
Jaguar QC amounted to driving the car around with someone sitting on the bonnet listening for noises.
The UK auto industry is not noted for leading-edge technology.
The only changes were tighter tolerances, as appropriate for modern tooling and gauging techniques.