I’m sure they’ll work fine.

Joe is right. Nails have a higher shear capacity than a screw of the same relative size, but screws have a higher pull out value. Screws are usually harder than nails and therefore more brittle.

Makes sense on drilling a hole

Picked up this box this afternoon from Russel Do It Center and going to slather up the two boards with Loctite PL Premium
Should work well.

Glad to be doing this project in March rather than August

I might consider predrilling 1/4" holes in the scab boards to keep them from splitting. 5/16" is a big screw.

I know that virtually no one trusts glue and always wants to glue and screw, but I had an old wooden boat builder with years and years of experience tell me one time:

"If glue won't hold it a screw damned sure won't hold it."

If anything a screw should be placed in there to pull the wood together and hold it until the glue dries. Think of it this way... Once the glue dries, the glue is providing shear resistance across the whole faying surface. Screws are only providing shear resistance across the shaft of the screw.

When a laminate traditional bow is made or a laminate wood beam is made, there are no screws... Only glue.

Glue is badass. Screws... Meh...

So either screws or glue, but you really don't need both. Like I said each one of those screws will provide about 400 pounds of shear resistance. So 4 of them on each side of the crack would be more than enough.

If I was fixing that, I would cut 2 pieces of 3/4" plywood the same depth of the rafter and make them long enough to extend 12" on each side of the crack, dampen both surfaces, then glued the chit out of both surfaces with Titebond III, clamp them on each side, let dry, take the clamps off and go have a beer.

Just wrap it with duct tape and add a couple zip ties.

If you use a GOOD glue and plenty of it , you can take the screws or nails out and throw them away after it cures.

Small brush to get the glue in the crack. I would then put a board under the cracked one and pry or jack it up to close the crack and align it up with all the other rafters. The half inch plywood on each side, as Irish mentioned, with screws should give you many years of trouble free support. Don’t forget to remove the jack. And get it done before your attic gets any closer to 120 degrees.

2 pipe clamps and a truck antenna is all you need

Zip ties darn it.

What are you going to use to whip somebody's ass then?

A good constitution adhesive and zig zag the screws

On a different note I watched an old carpenter craftsman build a 16” x40’ structural beam many years ago out of plywood glued and nail gunned together about 8” thick. I was amazed at the time. Didn’t realize glue lam beams would become a common thing

You might also kick off a brace up to the rafter from the joist under it . It may have been a cracked or damaged piece of wood when nailed up and just split more. Unless it's opened up really big and sagging , it may not be as bad as it looks . Prolly not a big deal , easy little fix.

How did you discover this attic rafter with a crack in it?

Putting decorations in the attic, I’ve known about it for a while just been lazy on getting it fixed.

It’s a fairly small crack so I wasn’t super concerned

Back in the 80s we bolted steel plates between 2x10s to get a 40 ft span for a second story balcony

Used 8 of those 4” screws, right as I completed driving the last one the tip snapped off the included T30 bit.
Ended up driving 2 extra 3” deck screws.
Went very liberal with the PL Premium.

Should be a good enough fix, worse case that rafter ends up getting replaced but I doubt that will be necessary.

That ain’t a rafter but I think you’ve got it fixed.