This 20-piece bolt and washer fastener kit is built to secure Mercury Racing high-performance cylinder block halves at the ten exterior fastener locations (five per side). These are the threaded screw/bolt holes around the outside of the block that clamp the two block halves together and help maintain proper sealing and alignment under high RPM and high cylinder pressure—2.5L Mercury Racing V6 powerheads.
It’s a strong fit for the popular Mercury Racing performance families most builders search for, including 245 HP, 260 HP, 280 HP, 280 ROS, and 300 Drag cylinder blocks. Whether you’re doing a fresh build, replacing mismatched hardware, or refreshing a tired powerhead that’s been apart multiple times, having correct, consistent fasteners at these exterior clamp points helps deliver more uniform torque and more reliable long-term clamping.
The kit includes ten (10) 12-point specialty bolts—3/8-16 x 1-1/4 in. 12-point Alloy Steel (170,000 PSI Tensile) yellow zinc screws—chosen for secure tool engagement and repeatable torque-up. It also includes ten (10) thick case-hardened stainless washers sized .401 x .745 x .097, which spread the load, protect the block surface, and help reduce washer “dig-in” during assembly and heat cycling.
This fastener kit replaces Mercury OEM part numbers 10-8231991 and 12-822838, making it easy to match to common parts lists and rebuild notes when you’re servicing Mercury Racing high-performance block halves.
Mercury OEM part numbers 10-8231991 and 12-822838, MSRP $97.89
Contact mike@buckshotracing77.com or +1-714-697-1716 with any questions.