Now, 3DES comes in two main flavors:
The "2 key" version; in this version, the 3DES key consists of two DES keys; k1 and k2, and we implicitly assume that k1=k3. DES keys are typically represented in 64 bits, and so this version of 3DES has 128 bit keys.
The "3 key" version; in this version, the 3DES key consists of three DES keys; k1, k2 and k3. Because all three 3 DES keys are explicitly represented, this version of 3DES has 192 bit keys.
The keys are sometimes also referred to as key A, B and C. The key for the 2 key version is then referred to as an ABA key and for the 3 key version as ABC key.
Those are the only standard versions of 3DES; you might have an API which allows 64 bit keys (which likely emulates DES in that case); if it allows 256 bit keys, I have no idea what it would do with them.