Mystery Bit Fallen Off

[slowmotion]

I've been fiddling with two bikes, on and off, for the last few days. Brakes, shifters, front and back derailleurs and bottom bracket. I found this widget in my cycle jacket pocket, and I have no idea what it is or how it got there. It may have nothing to do with bikes, but it makes me a bit nervous.

It seems to be BZP steel, 11.5 mm diameter, 7mm tall with a hex socket 5mm AF, and a 4mm through hole. There are two bits which screw into each other.

If anybody knows what it is, I would be really grateful if they could set my mind at ease.

Thank you.

 

[Cubist]

Looks like a chainring bolt.
It looks like you put it together wrong. The slotted side fits into the ring from the spider side, , threaded part uppermost and slots at the bottom. The part with the hex fits in from the other side, the flange holding the ring in place. Te slots are to hold it steady with a special tool while you tighten it with a hex key.

 

[Cubist]

Here's a pic from a wiki page on cranks



A chainring bolt. These are used in various lengths both to join rings and to fasten the assembly to the spider of the crank. While some have recessed hex fittings in both screw and nut, some like this have a slotted nut that allows the use of a special tool.

 

[AndyWilliams]

Is that not this bit ??

 

[I like Skol]

As Cubist says, most likely a chainring bolt, but also often used to fix rear derailleur hangers to the frame. You say you have been fiddling with the gears so did you remove the hanger at any point?

 

[slowmotion]

Looks like a chainring bolt.

Holy moly! I changed the middle chainring too and stuck the bolts in an ultrasonic bath. I think I may have been entirely stupid and not put them all back in. That might explain why my indexing of the front mech has been a total disaster. I will report back. I'm really grateful!

 

[Cubist]

 

[slowmotion]

As Cubist says, most likely a chainring bolt, but also often used to fix rear derailleur hangers to the frame. You say you have been fiddling with the gears so did you remove the hanger at any point?

Yep, I put in a new one. I'm fairly sure that the new hanger came with another insert like the Mystery BSO, so that may be the answer. Thank you.

Is that not this bit ??

I didn't touch the rack mounts but I did fiddle with the bottle cage mountings. I seem to be turning into Captain Calamity!

 

[slowmotion]

The chainring bolts are black, not BZP. Even with my failing eyes and stupidity, I'm pretty sure I would have noticed a missing one. I'm betting on the hanger/dropout insert.

Time will tell.

Thank you for your advice, you lovely people.

 

[slowmotion]

It's definitely the hanger fixing bolt and insert. I took the new hanger out of its packet and lined up the holes with my old hanger in order to check I was buying an accurate replacement. I must have put the new bolt in my jacket pocket.

 

[I like Skol]

It's definitely the hanger fixing bolt and insert. I took the new hanger out of its packet and lined up the holes with my old hanger in order to check I was buying an accurate replacement. I must have put the new bolt in my jacket pocket.

So I win! What's my prize? Don't rush, as long as it arrives at Skol Mansions before weekend I'll be happy....

 

[slowmotion]

{ assumes Alec Guiness-like voice as the sage in Star Wars...}

"Your gift is sharing The Knowledge"

BTW, Does Skol still exist? For some reason, in tins, it was very popular with yachties in the 1970s.

 

[Cubist]

​

 

[I like Skol]

BTW, Does Skol still exist? For some reason, in tins, it was very popular with yachties in the 1970s.

I hope so because I drink it by the gallon!!!

 

[Fab Foodie]

Holy moly! I changed the middle chainring too and stuck the bolts in an ultrasonic bath. I think I may have been entirely stupid and not put them all back in. That might explain why my indexing of the front mech has been a total disaster. I will report back. I'm really grateful!

... and I thought it was that nut holding the handlebars ....