FLEXI (FX)
Non-polarized 
#555
2 SMD
5050
AC 6.3V
 
Non-polarized means they will work placed in the socket in either direction.
Older & less expensive bulbs would have to be placed in the socket in one direction.
They are high quality 5050 SMD bulbs. Not the weaker 3528 used by many pinball led companies.
 
3528 LED
Dimensions 3.5 mm x 2.8 mm
Chip Surface Area 9.8 mm²
Lumen Flux 6-8 lumens
Power Consumption 20-30 mA @ 2.8-3.4 Volts
 
5050 LED       
Dimensions 5.0 mm x 5.0 mm. 25 mm²       
Chip Surface Area 25 mm²
Lumen Flux 16-22 lumens      
Power Consumption60 mA @ 2.8-3.4 Volts
 
5630 LED      
Dimensions 5.6 mm x 3.0 mm. 16.8 mm²    
Chip Surface Area 16.8 mm²
Lumen Flux 45-50 lumens      
Power Consumption150 mA @ 2.8-3.4 Volts
 

These work great in a horizontal socket