I'm talking about something like this Type LB Conduit Body
Only then can the conduit body contain splices.
In your specific case, I don't see the volume listed in the specifications section on the Home Depot page. So you'd have to check the fitting itself, to determine if the manufacturer has marked the volume. You didn't say what size wires you're pulling, so I can't answer that definitively. You also didn't mention the number of conductors, so it's impossible for me to do the fill calculations.
Examples of short radius conduit bodies
Box Fill Calculation
For each current carrying conductor that terminates within the box, you'll add 1. So if you're pulling one ungrounded (hot) conductor, one grounded (neutral), and one grounding conductor. If you want to splice within the box, the calculation would look like this.
Ungrounded (hot) 1 Ungrounded (hot) 1 Grounded (neutral) 1 Grounded (neutral) 1 -------------------------- 4
If grounding conductors are used, you'll add 1.
Current Carying 4 Grounding 1 -------------------------- 5
Once you have the conductor count, you'll use Table 314.16(B) to determine the required volume.
NOTE: You'll always base the calculation off the largest conductor used. so if you have a #14 grounded (neutral) and a #12 ungrounded (hot), you'll use 2.25 because of the #12. If you're using grounding conductors that are a different size than the current carrying conductors, you'll multiply them separately (#12 hot, #12 neutral, #14 ground = 2 x 2.25 + 1 x 2.00).
If the largest conductor used is 14 AWG, you'll multiply the conductor count by 2.00 according to Table 314.16(B).
`5 * 2.00 = 10.00'
Which means the box must have a volume of at least 10 cubic inches, if you want to splice within it.
If the largest conductor used is 12 AWG, you'll multiply the conductor count by 2.25.
So in this case, the box must have a volume of at least 11.25 cubic inches.
3 Ungrounded (hot) Conductors
If you were pulling 3 ungrounded (hot) conductors, the calculations would look like this.
Ungrounded (hot) 1 Ungrounded (hot) 1 Ungrounded (hot) 1 Ungrounded (hot) 1 Grounded (neutral) 1 Grounded (neutral) 1 Grounding 1 -------------------------- 7
12-2 will work, 12-3 is too much.
If you are using a 3/4" Carlon, it's 12 cubic inches and should be marked. 12-2 with ground, spliced, needs 5X 2.25", 11.25 cubic inches, passes. 5 is two neutrals and two hots that terminate in the box, plus one for the ground. 12-3 with ground needs 7X 2.25, 15.75 cubic inches, fails (unless you increase to a 1-1/4" LB with 32 cubic inch volume).