So I have a 21" Trek 930 MTB where the reach is a bit too far, trying to make it fit as a commuter because it's a really nice ride other than that. I pulled this stem off of it (https://imgur.com/gallery/5KGDB) height seems ok but I want one that is about half as long like where the black lines are. can anyone recommend a stem that would work? I know it's not the standard size, sorry I am new to bike mechanics.

Here is one that is 65mm long. Double check that it matches the clamp and quill diameters of the stem you have now.

Other options are to change the bars to a style that sweeps back, or get a 1-1/8 to clamp on style adaptor. Then you can chose from many very short stems.

Yours is pretty short and can be adjusted upwards at the pivot, if your cables and housing have enough slack.

Otherwise, bring the bars up for easier reach with the stem below.
https://www.niagaracycle.com/categor...ilver-anodized

Add a Bell cabling kit if you need to add longer cables.
https://www.walmart.com/ip/Bell-Bike...e-Set/17619556

Like Insidious C mentioned, you need to figure out what size quill and handlebar clamp you need before selecting a replacement. The length doesn't matter if the part won't fit your bike.

The quill is the part of the stem that sticks down into the fork's steerer tube. The outside diameter of your fork's steerer tube will be either 1" or 1 1/8", and a stem's quill will be sized for one or the other. They're not interchangeable. If you don't have calipers or a ruler handy to measure, you can check the size by using a U.S. or Canadian quarter. A quarter will fit into a 1 1/8" steerer, but not into a 1" steerer.

Canadian quarter = 23.88 mm
U.S. quarter = 24.26 mm
Diameter of quill for 1" steerer = 22.2 mm
Diameter of quill for 1 1/8" steerer = 25.4 mm (1")

As for the other dimension, handlebar clamp diameter... You may want to measure to be sure, but I'd feel pretty safe guessing that if your bike's old enough to use a quill stem, it'll have a 25.4 mm (1") handlebar diameter. That was a pretty standard size for flat bars like you'd find on mountain bikes. There are probably exceptions to the rule, but bigger diameters like 31.8 mm came into general use after the industry moved from quill stems.