To pull small strips of bacon through lean roast, you can use a larding needle or a larding pin. The latter has a long (approx. 30-40 cm) and narrow semi-cylindrical shaped blade with a sharp point, fixed in a wooden or plastic handle. A strip of bacon or some chilled fat is placed in the tray after the larding pin has been cut right through the meat. When you pull back the larding pin, it is turned over and the fat is left in the meat.
The larding pin used on large cuts of meat would have a spring and lever to cut the strips and hold them in place (1).
The trussing needle and larding pin are kept in a typical set of 2 needles and 12-15 awls of different sizes (2). [MOT]
(1) "Nouveau Larousse ménager": 693.
(2) CHANCRIN & FAIDEAU: 736.