4.5mm Hydraulic Union Thread Size?

Post by **CitroJim** » 26 Jun 2011, 22:26

I am in the process of constructing a hydraulic pressure gauge to tee in the output of a pressure regulator to enable hydraulic line pressures to be read.

I need to construct a 4.5mm union socket to accept the hydraulic pipe flare that's normally screwed into the pressure regulator body.

I thought at first it was M8 but it's not. Although the thread of the union is the same pitch (1.25mm) as standard M8 the diameter of the thread is about a mm larger.

Try as I might i just cannot identify the thread in order to determine the tap I need. I've gone through all the thread data I have and no joy. It's not BSP (British Standard Pipe) as I thought it might be. Maybe it's FSP (French Standard Pipe)

Does anyone know and additionally know a supplier of a suitable tap?

Thanks

This is a bit of a showstopper right now...

citronut · Post by **citronut** » 26 Jun 2011, 22:38

i think the staderd pipe nut thread on the 3.5mm pipe is 7mm 8mm spanner size,

as i have in my tool box a tap for cleaning up damaged threads in the likes of suspesion cylinders,

not sure on the 4.5 but they are usualy 9mm spanner size as im sure you know, so it must be 8mm thread diamiter,

have you not got a nut from a 4.5 pipe you can try through some die's,

if not i will see if i have one and the apropriate die tomorow,

regards malcolm

Post by **CitroJim** » 26 Jun 2011, 22:44

That'll be great Malcolm, thanks

All I know is it's not a standard thread size...

addo · Post by **addo** » 27 Jun 2011, 09:55

9 mil metric fine?

Are you selling these tees?

Post by **CitroJim** » 27 Jun 2011, 11:18

addo wrote:9 mil metric fine?

Are you selling these tees?

Nope to both Adam..

I thought about 9mm Metric Fine but it does not appear to be... 9mm MF is bigger in diamater by about 1.5mm. Imagine something between Metric Coarse M8 and Metric Fine 9 and you're there. The only similarity is that all have a 1.25mm thread pitch...

If I succeed then maybe I will offer clones or at least a design. It could be a very handy tool to confirm regulator health and so on.

citronut · Post by **citronut** » 27 Jun 2011, 12:38

well the closes i could get it to nearly thread into was a 10x1.5 die, still not right though, take it along to a machine shop they will you'd think be able to tell you the thread dimensions,

as they you never know might have a wider selection of tapps and die's than you Jim

regards malcolm

addo · Post by **addo** » 27 Jun 2011, 13:27

Jim, don't know if you have bookmarked this page or not but I often refer back to it for thread ID:

http://mdmetric.com/tech/tict2011.htm

kenhall1202 · Post by **kenhall1202** » 27 Jun 2011, 14:46

I think it is a typical Citroen 'odd man out' type thread, most probably 9mm X 1.25 Metric coarse. See http://www.newmantools.com/ and look under 'technical stuff'. 3.5 mm pipe nuts use an 8 mm X 1.25 Metric coarse thread I think.

RDGtools.co.uk will sell you a set of three 9mmX1.25 carbon steel taps for £5.94 (Cheap and cheerful probably made in India!). I bought a 14mm X 1.5 tap set from them for cleaning out the thread lock residue when refitting the crankshaft pulley to my 2.1TD.

The use of 7mm metric fine bolts is also a Citroen oddity - I had to source some to make a puller for removing my Epic diesel injection pump toothed pulley.

Post by **CitroJim** » 27 Jun 2011, 19:49

Ken, that's brilliant

many thanks...

It's positively identified, thanks to the Newman Tools website as an M9 coarse. The 3.5mm one is indeed M8.

I've just ordered a set of M9 taps

The data I was using was in my old 'Zeus' book, a happy companion to any engineer, and that neglected to mention that M9 even existed....

The project can now continue.

Ken, many thanks again

This forum really does come up trumps when you need it most...

citronut · Post by **citronut** » 27 Jun 2011, 20:31

im prety sure the 3.5 pipe nuts are 7mm thread, i will double check my tap in the morning at the one i bough many years ago specificly for cleaning up threads in GS/CX suspension cylinders,

regards malcolm

Post by **CitroJim** » 27 Jun 2011, 20:36

citronut wrote:im prety sure the 3.5 pipe nuts are 7mm thread

No, definitely M8 on a Xantia Malcolm. I just ran a 3.5mm union down an M8 nut....

Maybe the CX/GS used a different size of 3.5mm union?

Pleiades · Post by **Pleiades** » 27 Jun 2011, 22:14

Jim and all.

For reference.

3.5 = M8 X 1.25
4.5 = M9 X 1.25
Old 6.35 style M12 X 1.25
New 6mm (xantia pump) M12 X 1

Regards.
Martin.

Deanxm · Post by **Deanxm** » 27 Jun 2011, 22:27

Pleiades wrote:Jim and all.

For reference.

3.5 = M8 X 1.25
4.5 = M9 X 1.25
Old 6.35 style M12 X 1.25
New 6mm (Xantia pump) M12 X 1

Regards.
Martin.

Thanks Martin, ive made a note on my shed wall for future reference

D

Post by **CitroJim** » 28 Jun 2011, 06:41

Martin, many thanks indeed