i have a trek marlin 29er.

i want to get an adjustable stem for it.

stats on the marlin -
https://www.trekbikes.com/us/en/bikes...r_sport/marlin

the stem im looking at -
https://www.amazon.com/Zoom-25-4mm-Ad...8754483&sr=8-2

it's a 25.4mm but it asks about a 105/41mm or 85/41mm size...i'm not sure which i need or what this size is referring to.

can someone let me know what measurement this is?

thanks in advance!

The 105 and 85 likely refer to the length of the stem. Usually the length of the stem us measured from the centre of the steerer tube clamp to the centre of the handlebars.

The 41 which appears in both sizes may be the height of the stem, or of the clamp, but I'm not sure.

It is likely that both sizes will fit, or not fit. What you need is a 1-1/8" threadless stem with a 25.4mm bar clamp. Any 1-1/8" threadless stem with a 25.4mm bar clamp will work on your bike. THe ad you linked does not specify that the stem is a 1-1/8" threadless stem, but since that has been the standard size for all bike-shop quality bikes for the past 15 years or so, it may be safe to assume that is what it is.

In fact, the older standard size, 1", uses a 25.4mm steerer tube clamp, so maybe that is what the "25.4mm" in the description is talking about.

I suggest you call the vendor, or go the LBS and pick up an adjustable stem there. It will likely be the same price or cheaper.

The 25.4mm is not the steerer tube size, but the handlebar diameter size, this is an old standard, which is being replaced by 31.8mm & 35mm handlebars. The Steerer tube will be 1 1/8th" as has been standard for the last 15 years, although is being slowly replaced by tapered.

Looking at the stem from Amazon, that will mess up the ride characteristics of the bike, modern MTB's are designed to use short stems, anything over 90mm will be way to long for that bike, guessing it comes with one between 60-80mm which will be right for it, also, if you are taking the bike off road like it's designed for, you are introducing another area to fail unnecessarily.

If you need to change the handlebar height, would look at riser bars with a larger rise than the 5mm which is stock.

Found this on another site:

The Zoom Adjustable Stem gives you quick and easy handlebar height adjustment.

• Zoom Ahead stem
• 3D forged alloy
• Color: matte black
• Sandblast with silver sandblast top clamp
• 1.1/8" x 28.6 mm
• Ext.: 120 mm
• Bar bore: 25.4 mm
• Stack height: 41 mm

QBP stocks one similar [any LBS with an account can Order one],

yes 2 extension choices,8 short,and 10 long.
then you choose the bar clamp diameter, straight bar , 1" aka 25.4mm.
and Road bars, 26.0mm ..

Ditto Richey..