i read on Futaba's site that the only one that in the spec talk about metal gear is the Futaba BLS351 Digital High Torque Metal Gear .
The 251 is a gyro servo ..maybe on elevator......and the 451 (that I orderd) has not this in the describsion...
I dont say that you have wrong Kjell.....but this is what i have found!
Check site
351
http://www.gpdealera.com/cgi-bin/wga...pgm?I=FUTM0551
451
http://www.gpdealera.com/cgi-bin/wga...pgm?I=FUTM0552
251
http://www.gpdealera.com/cgi-bin/wga...pgm?I=FUTM0550