This post will explain to you, how to split or join .001, .002, .003 etc. files.
First, to split or merge these kind of files, you need to install a package called lxsplit. For that, type
apt-get install lxsplit
lxsplit -j filename.001
Note: filename.001 should be the name of the first file including extension.
Split a file into pieces
lxsplit -s hugefile 15M
hugefile should be the name of the file with extension and next option should be the size of the each file after splitting. M denotes MB and other split size examples are 5000k, 30000000b.