Target sight adjustment slot length & width?

SOS: I have been unable to find any decent screwdrivers for the sight adjustment. Probably the same size for elevation & windage, so I need to modify a couple of mine. I have calipers & can read them, but can't see the slot enough to get the calipers in them without scratching everything. Wilson, Bo-mar, SA, Baer PII, & ED ET. Thanks in advance.

I always used the old smith and Wesson revolver screw drivers

Many thanks for the info, Chris, I didn't even know that S&W made or sold screwdriver sets. I modded one of my Craftsman by lapping down the blade faces to the correct "fit like a glove" philosophy   but the width was a tad too wide so I gave it to my shooting partner to grind down the sides a tad & he like lapping work so much he kept them and now claims he does not have it & that he does not remember me giving them to him. I'm working on a budget here, unfortunately. Time for a new screwdriver and a new shooting partner.

These bits are good for thin blades
https://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/screwdrivers-sets/magna-tip-bit-sets/magna-tip-thin-bit-set-prod44342.aspx

But they are not real tough for torquing.  They can twist at the tip.

If you want the best, get Snap-on electronics line

https://m.ebay.com/itm/VINTAGE-SMITH-WESSON-REVOLVER-PISTOL-FACTORY-SCREWDRIVER-SIGHT-ADJUSTMENT-TOOL/163181991487?hash=item25fe67963f%3Ag%3AHWoAAOSwq2pbQQiB&_nkw=s%26w+intage+screw+driver&_from=R40&rt=nc&_trksid=p2380057.m4084.l1313.TR12.TRC2.A0.H0.Xs.TRS2

Many thanks, Chris. I ordered the 1 for 29.XX. I should have it by the 9th. E-Bay confirmed the order, so I guess it's mine. God Bless all. I was just getting ready to post up what a !@#$%^ it was modding a screwdriver & lapping the blade flats flat. My bud's going to ber super PO'd when I pull out my screwdriver at the range & adjust my sights. & tell him "no" because he has my original modded screwdriver.

Wonderful insights , thank you. 

It sounds like to me that the FFIII might work in terms of budge and warranty. 

It sounds like if I do an EGW mount I will avoid some issues. 

Do you think I can shout them with a #13 recoil spring? 

Sounds like, If I use a rib and mount it on the rib to test and If I like it then go full monty with the bomar mount.

found this too 

http://stores.kensight.com/kensight-sight-elevation-and-windage-adjustment-screwdriver/