bolt question

Thanks!

Jonathan Fairbanks, AK

Your post reminded me of an interesting lesson I learned some years ago. The vast majority (if not all) of Honda and Toyota automotive engines have a 1/8-28 pipe thread tapping in the block for the oil pressure sensor. That's a British Standard Pipe Thread - 1/8-28 BSP. Unusual for a Japanese manufacturer to use what really is a British standard, but it's true. Most everyone that installs a tee or other fitting in that tapping to add an aftermarket pressure gage simply uses a US 1/8-27 NPT thread. I have had people INSIST that the tapping is an NPT thread. But it's not. One can, in fact, jam a male NPT into a female BSP (at least in that nominal size) due to the close pitch - only one TPI difference. That's not the correct method though. That's why adapters are made to do the job properly. The pitch difference is so close, you have to look carefully with a pitch gage but it is there.

Rod

My guess would be that it is a metric size bolt. A 6mm would be just a touch smaller than 1/4"; more like 15/64. The metric series also have different thread pitches so I would suggest you look for a 6mm bolt with the correct pitch. If you do not have a metric pitch gage, take your bolt to a supplier and get a bolt to match it.

Rod

thanks!!

That head size is interesting though. A new, standard 6mm hex head bolt has an across-the-flats dimension of about 0.386". It is for a normal 10mm socket or wrench. It is too large for SAE size 3/8" and too small for SAE size 7/16" sockets or wrenches. It is reasonably close to the 3/8" one though. If either the bolt head or the wrench was worn a little, it could fit.

I suppose it could be a "special" head size for some reason. Is there any potential for an interference with anything by using a little larger hex head? If not, I would forget about the head size and concentrate on getting a fit with the thread.