I’m building an Allez Sprint and stems are very hard to come by. I have a Tarmac stem that was a takeoff from an SL7 and I was wondering if it is compatible. Thanks for any input.

Except for newer Giant, threadless stems clamp to a 1 1/8" steerer and a 25.4 or 31.8 mm handlebar. Except 35 mm super size that now seems only to be used on downhill and enduro mountain bikes. If in doubt, use a caliper.

Different stems have different stack heights at the steerer, so when replacing, be prepared to change the spacer stack.

If the hole for the steerer tube is the same size and the steerer tube comes up the required amount then you should be good. Same thing on the handle bar side, unless you want to use different bars.

If you have them, try them. But only if you know how to properly put a threadless stem on. Park tool makes some decent instructions and vids if you don't know.

Pretty good bet the old stem will clamp onto the steerer, 1 1/8" is pretty common. But take a caliper and measure your bars (and perhaps the bar of the bike the stem came off) to see if it's compatible. You can get a spacer if the bars are smaller than the stem, but not much you can do about the other way around.