Thank you for your answers! I have just received an answer from the company:
"Cat: 40588-r001 is a rabbit monoclonal IgG antibody. We don't know the exact dimensions of this antibody.
However, IgG antibodies are "Y" shaped molecules. For most polycolonal antibodies, the size is considered about 10-20 nm. Monoclonal antibodies are similar. According to Horng et al. 2008, IgG molecule dimensions are 13.7 nm (width), 8.4 nm (height)"