hi guys,
i really hope you can help me out, im kinda new to the bike scene and since buying my singlespeed boardman roadbike from halfords ive decided i want to do a few mods to my bike, anyways my question to u is i want to fit a stem but before i purchase one, can anyone please help me out and let me know what size stem i may need? i want to keep the original drop handlebars which are currently on the bike its just the stem i want change so i can get that mean slanted look on my handlebars, i know i havnt given you guys any dimensions, thats because i dont know what dimensions are on my bike :S
so from the little bit of info i have given above, do you reckon you could possibly give me a idea of what size stem i would require? also is it a straight forward fit? just take off the old stem and fit the new one? or is there cutting etc to do?
also could you please answer what it means by 60mm 80mm and 100mm lengths? is that how far forward the stem comes out? so the 60mm size would mean the handlebars are more closer back, and the 100mm means the bar would be further away from the rider, right?
anyways i believe the fork is a 1 1/8 fork.

im sorry if ive messaged a whole lot of rubbish, but i would really appreciate a reply with some kinda help.

thank you very much

You need to know the handlebar clamp diameter, the length you want, and the drop angle. A picture would help.

FWIW- Unless it's uncomfortable to ride, you should leave it alone untill a bike shop tech can explain things to you in person.

There is no way to answer your question without more info. Stem's vary widely in length, rise, and size of handlebar they accomodate. The stem you should get should be driven by how the bike fits you -- combination of rise and length puts handlebars in position that you can comfortably reach while riding. Whether you want bars higher up, farther away, or closer to you, will determine stem you get.

To answer question about length, a 60mm stem will put handlebars 40mm closer to the rider than a 100mm stem. Stem length is generally measured from midline of the steerer clamp to midline of the handlebar clamp. As for the "mean slanted look", you may not want that if using a stem with very little or no rise puts handlebars so low as to make you really uncomfortable on the bike. Here is an article about stems. https://www.brightspoke.com/c/understanding/stems.html

It sounds like you have a threadless 1-1/8" fork so that takes care of the first spec. The other is the diameter of the handlebar at the clamp. With alloy drop bars it's usually 26mm, but might not be depending on the brand, so you should measure with a caliper right where it leaves the stem, or loosen the clamp and slide it over to be sure.

The 60mm, 80mm, etc refers to the length of the stem from center of the steerer to the center of the bar.

The angle definition is a bit tricky with most measuring the angle between the steerer and extension, and others giving the rise, which is the angle to the ground. When calculating rise they figure the steerer to be at 73°, so a 17° stem mounted with the small angle down would be horizontal, or have zero rise.

Other than matching the diameters at both ends, which is the correct stem for you depends on why you're replacing it in the first place. If you're trying to adjust the fit, you need to figure whether you want the bat farther or closer, higher or lower, and find the stem length and angle that gets it there. You can also fine tune the height by moving spacers from above the stem to below or vice versa.

I'd say get one of Look's adjustable stems.
they are articulated so you can ride the bike and see what different settings Feel like,
then buy a fixed stem in that configuration of angle and reach.

I'd personally call in at a Halfords store and ask the bike mechanics there as a first step.