If you put the new steppers in I would say save yourself some hassle and get the lovejoy couplers. They are really inexpensive, $20 total for the X and Z gantrys.
WW Grainger part numbers

Qty 2. 4X175 Shaft Coupler Body $3.62 each
Qty 2. 4X236 Shaft Coupler Body $3.62 each
Qty 2. 1X409 Insert, Buna-N $1.94 each

Subtotal $18.36
Tax $ 1.24
Total $19.60

Again, I fought my Z axis for 3 days till I got these, man, what a difference!

 

Nice find. Thanks for sharing! Looks like there is a local Grainger's store, very close to me. So I will make good use of the info.

-Kwok

 

Now those part numbers are for 1/4" stepper and 3/8" acme rod, if you are staying with 1/4-20 rod you need to use 4 of one part number and still need 2 of the Buna-N's