Pneumatic tube. Low (polypropylene, max 85..90C) or high (max 180C, tefzel) temperature versions available.
Size = 6/4 (6 mm external, 4 mm internal). It fits the "MPX4250AP" pressure sensor that you find under "Sensors".
Price is for 1m (=>quantity is length). High temp version is more expensive than the lower temperature tube, but recommended for engine bay.
5/3 (5 mm external, 3 mm internal) size is available (eg. for the MPXH6400 sensor), just write it in the order note, but only in low temperature (85C, polyamid) material. With the MPXH6400 400kPa sensor, you want to switch from 5/3 to 6/4 tube as soon as practical, with a VIV6453 type pneumatic connector.
See also:

• Pneumatic connector
• MPX4250AP