Rheem Gas Heavy Duty Water Heater Models 265 Litre and 275 Litre - Manual (Page 21)

INSTALLATION
21
SADDLING PIPE WORK
To prevent damage to the cylinder when attaching pipe clips or saddles to the
water heater jacket, we recommend the use of self drilling screws with a
maximum length of 12 mm. Should pre drilling be required, extreme caution
must be observed when penetrating the jacket of the water heater.
Note: Damage to the cylinder as a result of saddling to the jacket will void
the warranty.