FM / ftdetect

/usr/share/vim/vimfiles/ftdetect

Name	Size	Mode	Actions
modulefile.vim	114	0644	edit dl rm
stp.vim	127	0644	edit dl rm

Edit: /usr/share/vim/vimfiles/ftdetect/stp.vim (127B)

augroup stpfiletype au BufNewFile,BufRead *.stp set filetype=stp au BufNewFile,BufRead *.stpm set filetype=stp augroup end