Rear brake boss thread query.

[Flyingblind]

Hi there. I'm building a bike using bits I have lying around and off ebay. It's based on an old Saracen Xray Pro frame. It was all going swimmingly until I got to the rear brake bosses which were missing. Everything on Ebay is either M8 or M10. I figured it to be M10 as an M8 bolt slips straight through but when they arrived although correct diameter they turned about half a turn before jamming and would clearly strip the frame threads if forced further. The bosses bought fit into a Giant MtB frame fine so clearly the Saracen frame has a different thread pitch or some such. Any advice would be greatly appreciated.

 

[Yellow Saddle]

10mm bolts on bicycles are Metric fine. You probably have Metric standard or coarse which you're trying to screw in there. Your RD's pivot bolt/mount is M10 fine. See if that fits, then you will know.

 

[Flyingblind]

Ok, thanks. I will check that out.

 

[Flyingblind]

I've had a closer look. Compared to a standard M10 bolt the bosses I bought are M10 fine for sure. Not being well versed in bike mechanics I thought maybe they were designed to be a tighter fit than standard nuts and bolts so just went for it with an adjustable wrench and got one side tightened down ok. I have messed up the start of the thread a little on the other side so the boss is tilting over before it will bite so think I will have to get a suitable tap to clean it up a bit.

 

[Yellow Saddle]

I've had a closer look. Compared to a standard M10 bolt the bosses I bought are M10 fine for sure. Not being well versed in bike mechanics I thought maybe they were designed to be a tighter fit than standard nuts and bolts so just went for it with an adjustable wrench and got one side tightened down ok. I have messed up the start of the thread a little on the other side so the boss is tilting over before it will bite so think I will have to get a suitable tap to clean it up a bit.

Well, that's a good result. You didn't screw up the thread completely and, you learnt a trick or two.

 

[Flyingblind]

A little update on my brake boss problem. I ordered a tap to clean threads and I had also ordered another pair of bosses earlier specifically for an eXotic frame and they all arrived today. Out of curiosity I tried the tap against the boss treads and they did not match. However the tap did match the thread of the boss I had not put into the Frame yet.
Clearly the boss I fitted had cut it's own thread. No Biggie if I leave it as it is and not take it out again. I will use an eXotic boss on the other side as that was starting to bite nice and square.
I guess one set is M10 X 1 and the other M10 X 1.25.
The moral is not to buy a frame missing the brake bosses no matter how cheap it is.
Or missing the derailleur hanger as that was another saga to match one to the frame. Hundreds to choose from.
A set of thread gauges would have helped although not sure if one would have fitted inside the lug hole.

 

[Yellow Saddle]

A little update on my brake boss problem. I ordered a tap to clean threads and I had also ordered another pair of bosses earlier specifically for an eXotic frame and they all arrived today. Out of curiosity I tried the tap against the boss treads and they did not match. However the tap did match the thread of the boss I had not put into the Frame yet.
Clearly the boss I fitted had cut it's own thread. No Biggie if I leave it as it is and not take it out again. I will use an eXotic boss on the other side as that was starting to bite nice and square.
I guess one set is M10 X 1 and the other M10 X 1.25.
The moral is not to buy a frame missing the brake bosses no matter how cheap it is.
Or missing the derailleur hanger as that was another saga to match one to the frame. Hundreds to choose from.
A set of thread gauges would have helped although not sure if one would have fitted inside the lug hole.

Oh well, now you have a tap for every possible 10mm occasion for the rest of your life. I hope you managed to get the cheaper carbon steel taps instead of the considerably more expensive HSS taps. Keep it up. The world needs more people with taps and dies.

 

[Flyingblind]

Not quite. I have a tap for any future M10 X 1.00 occasion. Plus a now slightly bodged build. Such is life. And a couple of bosses with different threads to check any other frame I might find. Good lessons learnt as well. How could something as simple as a bike have so many pitfalls? Lol

 

[Yellow Saddle]

Not quite. I have a tap for any future M10 X 1.00 occasion. Plus a now slightly bodged build. Such is life. And a couple of bosses with different threads to check any other frame I might find. Good lessons learnt as well. How could something as simple as a bike have so many pitfalls? Lol

Things are getting better. Way back there were different BB threads (two still survive), all sorts of odd seatpost sizes (now down to 3 or 4), different pedal threads, strange stem /bar diameters and zillions of tyre/rim sizes.

 

[themosquitoking]

A little update on my brake boss problem. I ordered a tap to clean threads and I had also ordered another pair of bosses earlier specifically for an eXotic frame and they all arrived today. Out of curiosity I tried the tap against the boss treads and they did not match. However the tap did match the thread of the boss I had not put into the Frame yet.
Clearly the boss I fitted had cut it's own thread. No Biggie if I leave it as it is and not take it out again. I will use an eXotic boss on the other side as that was starting to bite nice and square.
I guess one set is M10 X 1 and the other M10 X 1.25.
The moral is not to buy a frame missing the brake bosses no matter how cheap it is.
Or missing the derailleur hanger as that was another saga to match one to the frame. Hundreds to choose from.
A set of thread gauges would have helped although not sure if one would have fitted inside the lug hole.

As a cure to your hanger problem, might i suggest http://gearmechhanger.com/

 

[Flyingblind]

I solved that ok by making a paper temperate of the recess the hanger has to fit in then holding it up to the computer screen against the photos of the hangers listed on line. The site you suggest was the most comprehensive and had the one I needed but Bankrupt bike parts had one for considerably less.
Unfortunately they sent one very similar but not close enough although the part number on the invoice was correct which threw me for a minute. They were quick to admit their mistake and sent the correct one by return which was perfect.