arp sells a stretch gauge thats accurate to .0005 ten thous. now for an example they list a stretch spec of .0063 for a 3/8 bolt. shouldnt they be accurate to .0001 to get that exact measurement?

They list a range to tighten to. Which is more than .0005 IIRC.

The ARP gauge is extremely accurate, if it reads in .0005" increments. You would not be able to tighten a rod bolt to an accuracy of .0001" by hand. Think of it this way: an average human hair is approximately .003" thick, therefore any gauge that reads in .0005" increments is equal to splitting a hair six times!

but you would need a gauge that would be accurate to .0001 to get a the exact stretch spec of the bolt which would be .0063 well if they only have the gauge thats accurate to .0005 should i stretch the bolt to .0065 or .006? is 2 tenths of a thous. gonna make a difference? im putting together a high horsepower big block together and i just want everything to be perfect. thanks

I am not familiar with ARP's rod bolt stretch specs, but my guess is that .0063 is the mean and the range is .0058 to .0068. You will be OK with the gauge that reads in .0005 increments. Considering the pitch of the fastener's threads, it is very doubtful that a human could get the stretch measurement accurate to anything less than .0005".

then why doesnt arp just list it at .006 instead of .0063

I think its like he said above, it's a range thing. .006 doesnt tell you if .0069 will be too much. .0063 is probably theoretically optimum, but .0065 will probably work.

Maybe edit you thread title to say "Mike, Bill or Tom, have a rod bolt gauge Q" or something, those three guys should be able to tell you what's a good range of measurements that will hold your bottom end in place.

i dont know if im being to picky here or what. i will just stretch the bolt at .006 then i will look at the gap on the gauge thats between .006 and .0005 and just put the needle at were i think
.0003 is. remember that this is a gauge thats accurate to .0005 im just syaing it would be nice if they sold a gauge that was accurate to .0001 so i could just stretch the gauge to .006 then go 3 lines more from that and that would give me a spec of .0063 which would be right on to arp specs.

is this making any sense?

Originally posted by RIPPERS 67:
i dont know if im being to picky here or what. i will just stretch the bolt at .006 then i will look at the gap on the gauge thats between .006 and .0005 and just put the needle at were i think
.0003 is. remember that this is a gauge thats accurate to .0005 im just syaing it would be nice if they sold a gauge that was accurate to .0001 so i could just stretch the gauge to .006 then go 3 lines more from that and that would give me a spec of .0063 which would be right on to arp specs. =
Ripper,
Yes, you are being too picky but that is a good habit to get into.
In this case you are worrying too much.
As has been stated most bolts come with a range like .0058-.0063 or some such thing.
Most stretch gauges come with a .001 reading gauge & this is more than adequate for what you are doing.
You can get to within a half thousands with a .001 gauge & closer with your gage & all you are doing is stretching a bolt not setting bearing clearance.
They also give you a torque value & if you compare the torque value they are saying is ok to the stretch value you will begin to realize how much more accurate stretching is.
People have been using a torque wrench forever & have very few problems but torque values are always conservative because you are measuring something like 20-30% load & the rest is friction which changes with surface condition, lubricant, thread condition etc.
As has been stated above, a half thou is about one sixth the thickness of a human hair & when stretching a bolt this is a bit of overkill.
Just stretch it to a tick over the .006 line & you will be fine.
I have been using a stretch gauge that reads in .001" for over 30 years & have never broken an ARP, Carr or SPS bolt which are the three biggies among the myriad of ones out there that are designed to be used with a stretch gauge.

When it come to picky or anal or whatever you wish to call it some think it's my middle name but there are places where a thou or a half thou are just fine.

This doesn't relate to stretching a bolt but when you get to tenths you need to take into consideration the temperature of the parts & the tooling used to measure & recalibrate your gauging before & during measurements unless you happen to be working in a controlled environment which most of us don't have the privilege of doing.

I recalibrate my bore gauge two or three times a hole when honing & it will change a few tenths during the day with temperature & use.
I let my race blocks sit a few hours & sometimes overnight before finish honing because they change size after honing, some over a half thou.
Point is some things need a lot of "pickiness",, some don't ;)
Just stretch the bolts to .006 plus a tick & be done. graemlins/thumbsup.gif

just like Mike said above torque ranges have a lot of variable introduced from the friction between the mating surfaces when tightening a bolt or nut. although it is much less than with torque there is going to be some variable due to the tensile strength of the fastener regarding how much it is going to stretch. each heat lot of material has a resulting tensile strength due to the variables in how it was produced. so a given amount of load will stretch two different grade 8 bolts a VERY slightly different amount. this is getting into the zone of minutia that is significant in a space shuttle bolt but not so much in a BBC. by the way, regarding the .003" reference above, does that also apply to the infamous RCH? LOL

Originally posted by 79943:
by the way, regarding the .003" reference above, does that also apply to the infamous RCH? LOL =
Hmmmmm,,,,
Just going from memory,,,, very old memory,,,
I believe those may be a bit thicker :D

Maybe a government grant is in order to do an independent scientific & very in depth study on these different standards of measurement :D graemlins/thumbsup.gif

thanks for excellent information you guys

Yes 79943, I think that some research into the RCH factor is needed here. I volunteer!!