NT-20-10HCVS 20” Singlehead Planer uses 2 spiral inserts.  The insert which comes on the 20" single head planer is a straight insert which measures 15mm x 15mm x 2.5mm.  It has vey small rounded corners, make sure you check the knife to determine if its straight.  The Northtech part # on the redbox  for the insert should be 15x15x2.5 SE  (straight edge)

The NT-20-10HCVS planer also can run the rounded insert 150mm tigra 101540, Northtech part # 15x15x2.5RE

Width=15mm

Length =15mm

Thickness=2.5mm

Holes 1 : 6.4 mm bore countersunk  

Edge : Straight

Corners : rounded

Single knife for each ten ordered, you get a free box

Made in Germany