DIY Balsa stripper

[g_kandylakis]

Temporary post to start a thread, so that I can use the thread link for an upcoming article in Aeromodeller. Please ignore for now, it will be locked until the article is published.

George

[g_kandylakis]

temporary unlocked, for a "simple" question.

What would be the closest equivallents in imperial units of the following metric items:

Allen screws (thread diameter and thread length)

M3 x 10
M4 x 12

M3, M4 nut (wrench width, thickness)

Thanks,

George

[TheLurker]

Can't speak for other anglophone countries, but in the UK I haven't seen imperial sized nuts & bolts available new for decades now so I'd be tempted not to bother with any conversions.

Even in the 1970s it was getting difficult to get older sized nuts & bolts new and in all our technical drawing lessons (1977 on) it was M4, M5 etc rather than 3/8" Whitworth, 2BA etc.

[TheLurker]

Just checked my tap & die set (bought very early 1980s) - all metric. 

However... it does have a card with some conversion to US standard sizes (NC, NF & NS)  in it.  Scanned copy too large to attach, will send in e-mail.

[g_kandylakis]

Thanks Lurk,

that is good enough too. So, this probably leaves the US out for now. If I get the info for US screws & nuts, I can modify the STL files. Otherwise they only stay metric.

[steve-de24]

Is this the data you are looking for?
UNC & UNF Threads

Steve

[g_kandylakis]

Hi Steve,

Thanks...

Well, yes and no, actually.

What I really need is the correct name of a 3mm and 4mm metric thread screw and nut, that one would easily find in a DIY shop in the US. And I have no idea which one that might be. Slightly smaller or larger is ok.

I cannot make this out of the charts, afraid of making a mistake. As easy as it is to read a metric chart for me, so is it very difficult to use a US chart.

George

And I need the dimensions so that I can modify the 3D printed parts for a US version.

[Nigel_M]

The US used to use 4-40 and 6-32 (iirc, and presumably 2-something and 8-something) for small aeromodelling bolts around 2-3mm such as engine mounting bolts or push-rod clevises, but would use UNC and UNF for larger sizes, such as an i.c. engine prop nut. I think the -40 and -32 are tpi. I'm sure our US hpa-ers will confirm the present situation though?

When I was heavily into CAD using Fusion 360, the software contained what was basically a nut/bolt/fastener catalogue from one of the major USA suppliers. Each item had a ready-made CAD diagram which you inserted into your design as a productivity aid. That might help?

[Nigel_M]

This site gives everything you need https://www.machiningdoctor.com/charts/unified-inch-threads-charts/ although possibly too much.

There is a table half way down 'Unified Inch Threads Dimensions Charts
UNC Series Basic Dimensions chart' that shows the 4-40 etc series is part of the same series as larger UNC. Table columns are headed Thread/Basic Diam/TPI/Pitch/Pitch Diam/Thread Height/Cres/ Root/Tap Drill Size/Lead Angle

CoPilot gives the following; apologies for the length.
"American bolt threads are standardized under the Unified Thread Standard (UTS), primarily using UNC (coarse) and UNF (fine) threads with inch-based measurements.
Overview of American Threads

American bolt threads follow the Unified Thread Standard (UTS), which defines a 60° V-shaped thread profile and is widely used in the United States and Canada for bolts, nuts, and other fasteners (ASME B1.1) . The UTS system is inch-based, meaning diameters and thread pitches are expressed in fractions of an inch and threads per inch (TPI), unlike metric threads which use millimeters .
Types of Threads

    UNC (Unified National Coarse): Coarser pitch, fewer threads per inch, used for general-purpose fastening .
    UNF (Unified National Fine): Finer pitch, more threads per inch, used where higher strength or precision is required .
    UNEF (Unified National Extra Fine): Extra fine pitch for specialized applications
    UNS (Unified National Special): Covers threads not included in UNC or UNF series .

Thread Designation

American threads are designated by major diameter and TPI. For example, a 1/4-20 UNC bolt has a 1/4 inch diameter and 20 threads per inch Machining DoctorMachining Doctor. Smaller bolts may use a numbered system (#0 to #12) for diameters below 1/4 inch .

Measurement and Identification

To identify an American bolt thread:

    Measure the major diameter across the outer edges of the threads.
    Determine the thread pitch in TPI.
    Use a thread gauge or reference chart to match the bolt to its standard designation .

Comparison with Other Standards

    Metric threads: Use millimeter-based diameters and pitch in mm.
    British threads: Include BSW, BSF, and BA, with different thread angles and pitch conventions .
    American threads are compatible with older NC/NF standards but follow the unified 60° profile agreed upon internationally in 1948 .

Practical Notes

    UNC threads are preferred for general construction and machinery.
    UNF threads are used in automotive, aerospace, and precision equipment

etc. Happy to help further if I can.
N

[Andrew D]

Can't speak for other anglophone countries, but in the UK I haven't seen imperial sized nuts & bolts available new for decades now so I'd be tempted not to bother with any conversions.

Even in the 1970s it was getting difficult to get older sized nuts & bolts new and in all our technical drawing lessons (1977 on) it was M4, M5 etc rather than 3/8" Whitworth, 2BA etc.

You can get UNC/UNC nuts and bolts in the UK without issue.  Some of our older gearbox designs at work have never been metricated and some of the drive line parts and engine bell housings are ASTM standards using imperial sizes.  Old Brit cars such as mini's or MG's were UNC and UNF (the mini ran to 2000) and suppliers to the classic car industry are a source of them in small quantities, also eBay has plenty of people selling them.  Anything made for British car industry by Joseph Lucas Prince of Darkness tended to be BA rather than the smaller UNC/UNF sizes, again a useful source...

Andrew

PS George.  If I can get you the CAD models for the smaller imperial sizes from our CAD library do you want them?

Andrew

[Jmk89]

I wouldn't worry about this issue, George.

McMaster-Carr seems to have plenty of suitable metric nuts and screws in suitable sizes: www.McMaster.com. 
They are a very big supplier of hardware in the USA and will supply hobbiest scale orders in my experience.

[TheLurker]

...Old Brit cars ...

Ahh, there you go.  The family Lurk gave up on UK designed motors in about '77-'78 and switched its alliegance from Hillman/Chrysler to Peugeot. No more faffing around with the Unholy Trinity of BA, Whitworth and AF for us.

[Nigel_M]

I wouldn't worry about this issue, George.

McMaster-Carr seems to have plenty of suitable metric nuts and screws in suitable sizes: www.McMaster.com. 
They are a very big supplier of hardware in the USA and will supply hobbiest scale orders in my experience.

Thanks, Jeremy, you've reminded me - it was McMaster-Carr whose catalogue is embedded within Fusion 360. Inserting any of their very extensive range of bolts and widgets into a CAD design is thus made extremely easy. Anything similar in your CAD weapon of choice, Andrew?

I think the question from George was what nuts & bolts would a typical modeller in USA find in a typically USA modelling shop. It will be useful if we can get an input from someone 'on the ground'.

[steve-de24]

George wrote "What I really need is the correct name of a 3mm and 4mm metric thread screw and nut, that one would easily find in a DIY shop in the US."

I think the style of screw that George is looking for is as shown in pic1 and the correct name would be :
M3 x 10 Hex Socket, Cap Head screw
M4 x 12 Hex Socket, Cap Head screw
Hex socket indicating the screw will be tightened with an Allen key and Cap Head defines the shape of the head.

The UNC equivalents would be :
#5-40 UNC x 3/8" Hex Socket, Cap Head screw
#8-32 UNC x 1/2" Hex Socket, Cap Head screw

Other thread types, method of tightening and head shape are available, see Screw types
(I've no connection with this UK company other than as a satisfied customer).

Steve

[steve-de24]

And does this answer your question regarding UNC nut dimensions  UNC Nuts
Steve