When looking at the 2051 Series of Gas Discharge Tube Arresters (GDT) from Bourns the individual part number will break down into 5 sections as shown in the below diagram from the Bourns data sheet. as you can see you can find the voltage of these from the second section. The number shown is the voltage divided by 10. ie 230v is represented by 23 in the part number.
Here is the 2051 Series data sheet.
Bourns® GDTs 2051.pdf (176.5 KB)
Applicable Part Numbers
2051-09-SM-RPLF 2051-09-SM-RPLF 2051-09-SM-RPLF 2051-15-SM-RPLF 2051-15-SM-RPLF 2051-15-SM-RPLF 2051-35-SM-RPLF 2051-35-SM-RPLF 2051-35-SM-RPLF 2051-60-SM-RPLF 2051-60-SM-RPLF 2051-60-SM-RPLF 2051-20-SM-RPLF 2051-20-SM-RPLF 2051-20-SM-RPLF 2051-23-SM-RPLF 2051-23-SM-RPLF 2051-23-SM-RPLF 2051-30-SM-RPLF 2051-30-SM-RPLF 2051-30-SM-RPLF 2051-40-SM-RPLF 2051-40-SM-RPLF 2051-40-SM-RPLF 2051-42-SM-RPLF 2051-42-SM-RPLF 2051-42-SM-RPLF 2051-47-SM-RPLF 2051-47-SM-RPLF 2051-47-SM-RPLF
2051-09-SM-RPLFTR-ND 2051-09-SM-RPLFCT-ND 2051-09-SM-RPLFDKR-ND 2051-15-SM-RPLFTR-ND 2051-15-SM-RPLFCT-ND 2051-15-SM-RPLFDKR-ND 2051-35-SM-RPLFTR-ND 2051-35-SM-RPLFCT-ND 2051-35-SM-RPLFDKR-ND 2051-60-SM-RPLFTR-ND 2051-60-SM-RPLFCT-ND 2051-60-SM-RPLFDKR-ND 2051-20-SM-RPLFTR-ND 2051-20-SM-RPLFCT-ND 2051-20-SM-RPLFDKR-ND 2051-23-SM-RPLFTR-ND 2051-23-SM-RPLFCT-ND 2051-23-SM-RPLFDKR-ND 2051-30-SM-RPLFTR-ND 2051-30-SM-RPLFCT-ND 2051-30-SM-RPLFDKR-ND 2051-40-SM-RPLFTR-ND 2051-40-SM-RPLFCT-ND 2051-40-SM-RPLFDKR-ND 2051-42-SM-RPLFTR-ND 2051-42-SM-RPLFCT-ND 2051-42-SM-RPLFDKR-ND 2051-47-SM-RPLFTR-ND 2051-47-SM-RPLFCT-ND 2051-47-SM-RPLFDKR-ND