These are available in all popular standards, BSP, ISO, UNF, and so on.
However, it is recommended to avoid styles with weakening thread undercuts whereby it can be useful to consider the following.
The required mounting space is not determined by the mounting thread but by the coupling thread.
On an installed test coupling the stud thread is not recognisable. Manufacturer’s recommendations regarding the mounting torque are therefor of limited value. More important it is to chose by principle a thread stud with a fracture torque that is above the torque that can be applied with a wrench.
A recommendation that, for an industrial application, tells differently is most likely the result of superficial planning. Even on the most compact control plates there is usually sufficient space to accommodate a test coupling which has a sufficiently robust thread stud. By a simple check one can verify that the torque that can manually be exerted through a wrench reaches approximately the value of 3 kpm. Therefor it is recommended to use test couplers which have the fracture torque of the thread neck considerably higher than this value. This at least in the general machine building sector. (In the Micro Hydraulics field other priorities might prevail)
The fracture torque for test couplers with various mounting threads are:
Mounting threads with high risks are:
M 12 x 1.5
M 10 x 1 - with shoulder sided seal undercut
M 10 x 1 - with radial seal
M 10 x 1 - with optimal strenght
BSP (G) 1/8" - with cylindrical thread
M 8 x 1 - with radial seal
The risk is be increased significantly through the notch effect resulting from shoulder seal undercuts. (Primarily on metric size threads)