Screw size problem for hub motor plates

[rg12]

I just noticed that my hub motor (big 4kw bike) plate is missing two screws (used to be just one...)
so I pulled all the 14 the were left (8 on each side) and put them back with locktite (because why would
the people of china bother to do that in the first place...)

Anyway, I am missing two of those little suckers. The hex socket is 4mm and the thread is 3.9mm (almost 10mm long).

How can I find these? When I needed screws for my rear brake rotor I just knew it's M5 screws but this one can't be M4 or something
since M4 is 4mm and not 3.9mm and on an M4 the hex socket would never be 4mm.

If we are on the subject, Is there such thing as M5 with a button head which has a socket bigger than 3mm? they strip very easy
those suckers...This screw that just came out of my hub has a 3.9mm thread and has a 4mm hex socket while my M5 screws
that have 5mm thread have those little 3mm hex sockets which are extremely small and strip very easily since my brake rotor
requires to tighten the rotor screws extremely tight.

 

[999zip999]

Don't use too long of screws as they could grind the inside of motor. Chinese screws can be anything that fits be careful as I found American nut fit on a crystalyte hub. Yes it was a machinist that found out ?

 

[rg12]

Hmm...I guess I would just have two spots that are missing a bolt...
Thanks man

 

[Warren]

Have you tried running a M4 bolt in the empty holes? That is what your 3.9 mm actually are. The top of the threads is just a bit flat.

http://www.mcmaster.com/#92095a190/=100fqpx

For M5 bolts, 3mm socket is standard, Chinese bolts often ignore the standards, like your M4s. I suggest getting Torx button head screws. They use a T25 socket. That is what comes with quality brake discs.

http://www.mcmaster.com/#92832a438/=100fx3s

 

[rg12]

Have you tried running a M4 bolt in the empty holes? That is what your 3.9 mm actually are. The top of the threads is just a bit flat.

http://www.mcmaster.com/#92095a190/=100fqpx

For M5 bolts, 3mm socket is standard, Chinese bolts often ignore the standards, like your M4s. I suggest getting Torx button head screws. They use a T25 socket. That is what comes with quality brake discs.

http://www.mcmaster.com/#92832a438/=100fx3s

You know what I will try to get a few M4's to check after reading that.
Thanks alot man!

 

[Mundo]

A little more exotic.

 

[rg12]

For my M5's I think I'm going to order titanium ones with torx socket as I already have a set
of quality torx drivers (something I really need to get for my allen wrenches...my chinese allen's are softer than butter!).

Thanks again guys,
Roy

 

[icerider]

For my M5's I think I'm going to order titanium ones

Titanium fastener will be OK going into Aluminum alloys and into most stainless steels.

There will be a relatively high corrosion risk going into mild steel.

 

[rg12]

For my M5's I think I'm going to order titanium ones

Titanium fastener will be OK going into Aluminum alloys and into most stainless steels.

There will be a relatively high corrosion risk going into mild steel.

Titanium bolts rust? Isn't titanium a kind of aluminum? I read in many places 'Titanium Alloy'...

 

[Chalo]

Exposed titanium doesn't corrode, but it's bad about exhibiting galvanic corrosion in many applications. There is special Ti thread compound that helps prevent this with a combination of lubrication and anodic protection.

Ti has no advantages in a fastener application, except lower weight than steel. In all other respects, it's an inferior material to steel or stainless for threaded fasteners. In your application, the weight of a few tiny screws is insignificant.

Use 18/8 stainless screws for non-magnetic, non-corroding, strong, reliable fasteners at a much lower cost than Ti.

 

[rg12]

Thanks alot I will look into that...I always thought that titanium is much stronger...Didn't know that it's all about weight saving.
There's that song Titanium by Sia...I thought that it's a way of saying how she is strong but I guess she just means light weight?

 

[Warren]

rg12,

Titanium is not a kind of aluminum. It is an metal element. Aluminum is a metal element. Iron is a metal element. They cannot be reduced further and still be an element. They can be alloyed/mixed with other elements to change their mechanical and chemical properties. Most metals in daily use are not in the their elemental/simplest form. They are alloyed with other elements to make them more useful. Alloys that were created early in human history have names all their own. Once people worked copper. When they discovered how to alloy it with small amounts of other elements it was much more useful and was given the name bronze, as in "bronze age." When we figured out how to work iron we got the "iron age." But when we learned to alloy it with carbon, we called it "the age of steel." "Stainless" steel adds a little chromium to prevent corrosion.

Our local recycling center has a sign saying, "this bin is for aluminum, and metal cans." It drives me crazy. :-(

 

[rg12]

rg12,

Titanium is not a kind of aluminum. It is an metal element. Aluminum is a metal element. Iron is a metal element. They cannot be reduced further and still be an element. They can be alloyed/mixed with other elements to change their mechanical and chemical properties. Most metals in daily use are not in the their elemental/simplest form. They are alloyed with other elements to make them more useful. Alloys that were created early in human history have names all their own. Once people worked copper. When they discovered how to alloy it with small amounts of other elements it was much more useful and was given the name bronze, as in "bronze age." When we figured out how to work iron we got the "iron age." But when we learned to alloy it with carbon, we called it "the age of steel." "Stainless" steel adds a little chromium to prevent corrosion.

Our local recycling center has a sign saying, "this bin is for aluminum, and metal cans." It drives me crazy. :-(

Thanks for the detailed explanation, that last line is a good one...

 

[Chalo]

Thanks alot I will look into that...I always thought that titanium is much stronger.

For the strongest normal fasteners, use metric class 12.9 screws. They're usually black.

 

[dogman dan]

Yes, take one cover screw to a good hardware store, then match it. Use the size check thingy to find the matching thread, then look for that size in the bins. Hex head, black bolts.

 

[rg12]

I wish the hardware stores around here would carry these...All they have is philips wood screws...
Nevermind, ordered some M4's to try out and black M5's with torx socket.

 

[Punx0r]

As a rule for generally making life easier and avoid frustration, use good quality fasteners (bolts/screws/nuts) and tools to drive them

 

[striider]

Exposed titanium doesn't corrode, but it's bad about exhibiting galvanic corrosion in many applications. There is special Ti thread compound that helps prevent this with a combination of lubrication and anodic protection.

Ti has no advantages in a fastener application, except lower weight than steel. In all other respects, it's an inferior material to steel or stainless for threaded fasteners. In your application, the weight of a few tiny screws is insignificant.

Use 18/8 stainless screws for non-magnetic, non-corroding, strong, reliable fasteners at a much lower cost than Ti.

Chalo - as usual, you are always a voice of reason and sanity. I must continue to dig through your old posts to glean more knowledge...

 

[dogman dan]

Hmm, time for your own hardware store. Buy a box of mixed size allen bolts?

http://www.ebay.com/itm/240pc-GRIP-Metric-Nuts-Bolts-Assortment-Kit-Washers-Hex-Machine-Automotive-Set-/131322118683?hash=item1e9368821b:g:AZoAAOSwAHZUPVu9

 

[rg12]

Me and ebay are good friends for almost 15 years now...