MWB is a Krautkramer Minature Angle Probe - 45 / 60 / 70/ 80 etc denotes the angle in steel and the 2 or 4 denotes the frequency- a crystal size of 8 x 9mm is used.
B is the code for a krautkramer 24,5mm dia compression probe
MB is the krautkramer code for a minature compression probe (10mm dia)
The frequency is denoted by the numerals 2, 2,25, 4 etc.
For example a minature 60 degree 4 MHz shear wave transducer will be marked MWB 60-4
Dent McIntyre and Andre Fouche are correct, the requested types are all Krautkramer probes, now GE Sensing & Inspection Technologies.
MWB 45 N4: Miniature angle beam probe, 45 degrees transverse wave in steel, 4 MHz;
B 2 S: Normal beam probe, longitudinal wave, 2 MHz, with soft protection layer;
MB4S: Miniature normal beam probe, longitudinal wave, 4 MHz, with soft protection layer.
You see, there is logic behind this nomenclature.
In NDT practice it is required to have a probe data sheet for each probe you want to use.
(Technical document from the probe's manufacturer) e.g. according to European standard EN 12668-2:
Non-destructive testing Characterisation and verification of ultrasonic examination equipment Part 2: Probes
the nomenclature you are listing was born in German.
These probes are manufactured by Krautkramer which is a company of the General Electric holding.
MWB45N4 is a "Mignon" (crystal size 8x9 mm), angled ("Winkel" is "angle" in german language), with Barium as crystal material, at 45° in steel refracted angle, "N" series and 4 MHz of nominal frequency.
B2S is a straight beam probe with Barium as crystal material, and 2 MHz as nominal frequency.
Further explanation could be met at GE website or on the probes data sheets.
These are old Krautkraemer probes (from the '70th). The characters mean in german language:
M = Miniatur (miniature),
W = Winkelpruefkopf (angle probe),
B = Bariumtitanat (piezo material = barium titanate),
45 = Winkel (probe angle = 45 degree),
N = Neu (new design, with LEMO plugs, in contrary to 'old' from the '60th),
4 = Frequenz (frequency = 4 MHz),
S = senkrecht (straight = perpendicular to surface).
Probe size of MWB45N4 should be about 10 mm x 12 mm,
Diameter of B2S should be about 24 mm, of MB4SN about 12 mm.
The probes are applicable until today in conjunction with LEMO plug equipped gear (except of B2S; this should be B2SN! The missing 'N' would indicate a historic plug very difficult to obtain today!).