Help with bolt size on cable shell guide

[Tony M.]

Hi, I need to replace the screw on the cable guide under the bottom bracket, maybe they call this a shell guide not sure, .Its on a 2002 De Rosa Merak , so don´t know if that makes a difference or perhaps they are all the same size on racing frames . I tried to measure it and I thought it was M5 ie. 5mm thread width but compared with another M5 I have to compare,  on my vernier measuring tool its actually about 1/2 mm less , any thoughts on this you mechanics out there ?The bikes getting repainted and all rusty screws and bolts being replaced with Ti this time .thks Tony

[puddings]

TonyHave you tried tastynuts - they do specific bike Ti and alloy bits (alloy may be lighter for none load bearing bolts). AFAIK most bike threads are slightly different to other engineering threads

[Richard Hallett]

Tony M. wrote (see). I tried to measure it and I thought it was M5 ie. 5mm thread width but compared with another M5 I have to compare,  on my vernier measuring tool its actually about 1/2 mm less , any thoughts on this you mechanics out there ?Better known as a 'very near' measuring device...The male screw thread will always measure slightly undersized because the crests have to be rounded off to provide clearance, typically by 10% as, in this case, the 0.5mm you measured. M5 it is.

[Tony M.]

Richard, You reckon this particular screw or bolt that holds on the the cable guide is the same size on most racing frames . The bottle mount screws are supposed to be M5 and its those that I measured and found to be slightly wider, yes only about .25mm wider but you  still notice the slack in the vernier caliper .I guess M5 is close enough so I´ll buy M5 and see  Just to say that I can´t try the screw in the hole as the frame is in Milan . thks Tony

[Richard Hallett]

Does the bottle mount screw fit the bottom bracket shell hole? If so, it is the same thread size regardless of the fact that one thread is slacker than the other. There is a lot of dimensional variation at the quality level we are talking about.