TexCoord1 = 5

UVs usually use Vector2 format. Vector2 uses two 32-bit floats; 8 bytes in total.

This vertex attribute maps to the semantic in HLSL. This UV channel is also commonly called "UV1". It corresponds to Mesh.uv2.

Additional Resources: Mesh.HasVertexAttribute, Mesh.GetUVs, Mesh.SetUVs.