Sensor sender - NPT 1/8 fitment

Hi,

I’m fitting some Stack gauges which come with sensors with 1/8 NPT fitting. When I fit into any of the various holes the sensor doesn’t wind in flush… is this expected? I get the same across various adapters - it’s just not something I’m used to.

Please see picture attached which is from a sandwich plate off the car - with oil temp and oil pressure sensors in pretty much as far as they will go.

is this right?

There are two different thread forms*, both the same pitch and nominal diameter - the sort you're used to will be a parallel thread, with the threaded length being the same diameter along it's length - this type requires a sealing washer, or gasket, of some sort. This will be the second type, with a taper to it, and the taper does the sealing (with a dab of thread sealant, or thread tape - some use a dab of locktite) - you can actually see the taper in the photograph.

Yes, it is perfectly normal. DO NOT use excessive force, it's possible to deform the housing or, in extreme examples of ham-fistedness, split the housing or shear the sender's body.

*NPT means National Pipe Thread, or NP Taper - depending on source. NPS means National Pipe Straight

The correct way to tighten an NPT thread, is this:

-- Turn by hand until just finger tight.

-- Use a wrench to turn 1.5 - 2.5 additional turns. The reason for the range is to allow for "clocking" of 90-degree fittings, for most things, just use 2 turns.

Also, with tapered pipe fittings, you want to use pipe sealant, such as Locktite 592 Thread Sealant (aka 592 PST Pipe Sealant with PTFE)

Great - thanks all for the quick response! So what I'm hearing is that this is normal but care must be taken to tighten up appropriately (and not to over tighten). First time I've encountered this on the car so thanks a lot!