Short answer: use a ring lug with an M8 mounting hole and a barrel made for your exact cable size. For the bolt, “M8” identifies only the nominal thread diameter.
Choose the lug by hole size and cable size
Battery lugs have two independent sizes:
lug size = cable-barrel size + mounting-hole size
For example, a product description formatted like “35 mm²–M8” normally indicates a barrel for a 35 mm² conductor and a mounting hole for an M8 fastener. The first value must match the conductor; the second must match the battery terminal hardware.
Check the lug maker's actual drawing or data sheet. A hole that is too small will not fit, while substituting a much larger hole reduces the contact geometry and can allow poor positioning. Do not assume that a nearby inch trade size is interchangeable merely because it looks close. Lug catalogs list conductor range and hole diameter separately; this terminal and lug sizing table illustrates that distinction.
Also match the lug material and construction to the conductor and installation. Use the specified crimp tool and die for that lug system. The correct hole and barrel do not compensate for a poor crimp or a cable that is not fully inserted.
Use the correct M8 bolt for the terminal
M8 identifies the nominal thread diameter. It does not, by itself, identify:
- Thread pitch
- Bolt length measured under the head
- Permitted thread engagement in the terminal
- Washer arrangement
- Tightening torque
Bolt length has to accommodate the complete hardware stack—the lug palm and any washer or other hardware required by the battery—while still providing the specified thread engagement. A bolt that is too short may not engage sufficiently. A bolt that is too long may bottom out in the terminal before it clamps the lug, making the connection feel tight when the lug is still loose.
Do not solve that uncertainty by adding random washers or forcing a bolt that binds. Compare a replacement with the supplied bolt or obtain the exact replacement specification.
A five-step fit check
- Read the cable size from the conductor or installation plan.
- Choose a lug barrel approved for that conductor size and class.
- Choose the same lug with an M8 mounting hole.
- Confirm the battery's bolt pitch, length, washer arrangement, and torque specification.
- Dry-check the stack before connecting the cable; the lug must clamp flat without the bolt bottoming out.
After installation, the cable should not pull sideways on the terminal, and the lug should sit fully on the contact surface. Use terminal boots or covers required by the installation.
Applying this to the Vipboss battery
The Vipboss 12V 105Ah Bluetooth LiFePO4 battery uses M8 terminal bolts. That answers the lug-hole question: select an M8-hole ring lug. It does not answer the cable-barrel question, because cable size depends on the installation's current, run length, routing, and protection design.
Keep the included terminal bolts if present. The supplied product information does not state a replacement bolt pitch, length, or tightening torque, so confirm those details rather than buying an arbitrary M8 bolt. The correct order is therefore: size the cable from the circuit, select the matching barrel, specify the M8 lug hole, and retain or verify the terminal hardware.
