A terminal stud or block has to match four things: the termination geometry, the thread, the current class and the voltage class. The geometry and thread are the ones buyers most often assume rather than check, and they are the ones that cause the connection to fail on the bench. Work geometry first, then thread, then current.
Step 1 — Geometry: square, rhombus or block
Square studs and rhombus studs are not interchangeable: the shape has to seat in the terminal recess or the lug that is already in the design. Rhombus studs (RH-80A and RH-150A) suit termination points shaped for them; square studs suit the square recess. A terminal block is a different connection type again, used where the termination is cable to cable or cable to bar rather than stud to lug.
If you are specifying from an existing drawing, the geometry is already fixed. If you are not, confirm it before ordering, because the wrong geometry cannot be adapted on site.
Step 2 — Single-thread or double-thread
The square stud range is supplied in single-thread (−ST) and double-thread (−DT) versions at the same current classes — for example SQ-120A-ST and SQ-120A-DT both exist. The choice depends on the termination method: a double-thread stud allows a second connection or a double-sided stack on the same stud. Pick according to how you terminate, not according to current, since the current class is available in both.
Step 3 — Current class, sized on the circuit
Studs run from 80 A to 400 A at 1000 VDC and terminal blocks from 50 A to 200 A at 600 VDC. Size on the maximum current the circuit will carry, and remember that the stud is one element of a connection: the lug, the cable and the tightening torque determine whether the joint actually carries that current. A 400 A stud with an undersized lug still limits the circuit.
The range at a glance
| Type |
Series |
Thread |
Current classes |
Voltage |
| Square terminal stud |
SQ |
Single (−ST) |
120 A, 150–200 A, 200–250 A, 300 A, 400 A |
1000 VDC |
| Square terminal stud |
SQ |
Double (−DT) |
100 A, 120 A, 200 A, 300 A |
1000 VDC |
| Rhombus terminal stud |
RH |
— |
80 A, 150 A |
1000 VDC |
| Terminal block |
TB |
— |
50 A, 75 A, 100 A, 200 A |
600 VDC |
What to verify before you order
- The recess or lug geometry the stud must seat in.
- The thread type your termination method needs.
- The maximum current the circuit will carry, plus its voltage class.
- The stud or block dimensions against the terminal you are replacing or mating with.
- The tightening torque and the standard your panel is built to.
Common selection mistakes
- Ordering a square stud for a rhombus recess. The geometry is not adaptable in the field.
- Treating −ST and −DT as equivalent. They are the same current class but not the same termination.
- Mixing voltage classes on one panel. Studs in this range are 1000 VDC and blocks are 600 VDC; the lower of the two governs the circuit.
- Sizing the stud but not the joint. Torque and lug selection decide whether the rated current is actually achieved.
