Determining thread bolt type

JimS · Oct 20, 2016

I lost a bolt to a difficult to access area. Without a plethora of replacement bolts to thread in, how may one determine or at least narrow down what type of thread the bolt hole is? Remember, I am talking about a bolt hole that is difficult to see into.

Thanks.

old · Oct 20, 2016

Maybe hard to find but they make a feeler gauge sort of thing that you use to determine tread for both blots ans pipe fittings. DG sent me one he had laying around and I have it right here on the desk so when and if I need it I can find it

Pair-a-dice farm · Oct 20, 2016

(quoted from post at 14:21:36 10/20/16) I lost a bolt to a difficult to access area. Without a plethora of replacement bolts to thread in, how may one determine or at least narrow down what type of thread the bolt hole is? Remember, I am talking about a bolt hole that is difficult to see into.

Thanks.

My bearing and bolt supply store has a set of plastic bolts that they will loan out to try in places like that. The plastic won't damage the threads if you try the wrong one. Knowing what type of equipment might help too. Many manufacturers use a standard type of bolt for each application. If this is on a piece of machinery, you might find a dealer that has the bolt or at least can tell you what you need

TimV · Oct 20, 2016

A few rather obvious things would be to narrow it down to inch or metric--granting some things are mixed but usually it's one or the other. Then inspect other bolts in the same area that do the same function, if any--they'll often be the same type. Another thought is that if it threads into cast iron it's probably coarse thread, which should also help narrow your choices down. Finally, just reaching in with small bolts and going up to larger ones will tell you quickly about where you need to be--you don't need to thread them in, just see if they drop down the hole and eliminate sizes at or below that one--a couple tries should get you mighty close. This may also give you an idea for length if the smaller bolt bottoms out.

Bill VA · Oct 20, 2016

Couple things come to mind. If you can get a pair of calipers to it, take an ID measurement and then look for something close from a thread dimension chart, that will get you in the ball park. The other is - if it's a tractor or implement, you might find a parts list online that gives you the exact thread size and length.

DGinVT · Oct 20, 2016

In my work I would never be without one.

Stephen Newell · Oct 20, 2016

If it's that hard to see into get one fine thread and one coarse thread and see which one easily threads into the hole using your fingers. The wrong one will stop you quick.

ss55 · Oct 20, 2016

You can use a thread gauge to determine the pitch.

Paul from MN · Oct 20, 2016

DG what is the tool you are referring to called?

DGinVT · Oct 20, 2016

I use a screw pitch gage which has pitches from 4 to 84 threads per inch. You can get them from ENCO, Travellers, MSC and KBC Tools. These guys are all on the internet.

JerryS · Oct 20, 2016

A set (or sets) of these might be helpful. These are both standard and metric, coarse thread, I think. Don't know many thread sizes are available.

MtMan · Oct 20, 2016

Do you know what size wrench fit the bolt head. If so you can guess the size of the bolt pretty well. As a 1/2 wrench will be a 5/16 and a 9/16 wrench the bolt will be a 3/8 bolt and etc. Then all you have to worry about is the length and either USS or SAE threads. Good Luck

Olliejunkie · Oct 20, 2016

if it is a piece of equipment you may find it in a parts diagram.

rustred · Oct 20, 2016

giving more details would help. like... cast , steel, plastic or ? and its pretty obvious that a 3/8 bolt wont go into a 5/16 hole and so on. and if its cast it will be course thread. so its not hard to figure out what bolt is needed. dont know if your talking caterpillar big.. or little stove bolts.

Craig45 · Oct 21, 2016

Is there another bolt the same size on your equipment?

GVSII · Oct 21, 2016

Most boxed tap & dye sets include a thread P/I and pitch gauge.If you don't have a tap & dye set you'll probably need one sooner rather than later.Some pretty good suggestions here on figuring out the bolt size and thread pitch of the bolt you lost.

Determining thread bolt type

JimS

Member

old

Well-known Member

Pair-a-dice farm

Well-known Member

TimV

Well-known Member

Bill VA

Well-known Member

DGinVT

Member

Stephen Newell

Well-known Member

ss55

Well-known Member

Paul from MN

Member

DGinVT

Member

JerryS

Well-known Member

MtMan

Member

Olliejunkie

Well-known Member

rustred

Well-known Member

Craig45

Member

GVSII

Member

Similar threads