Actually they are 3/4"-16 NPTP
However they fit 20 x 1.5 quite well, just do the up finger tight then 1/2 to 1 turn .
The B &S number is # 499532 Dia = 2.69" length =3"
or B & S # 492932 , dia = 3" length = 2.25"
and for the worry whorts
1.5 mm pitch = 16.9 tpi
3/4" = 19. mm
Oil filter threads are quite sloppy and they usually interchange quite well.
I fitted an Emgo Triumph oil filter base which came with CV2 metric filter and it ran mower filters just fine.
The specs are almost identical
20µ to 30µ filter 9 to 15 psi bypass valve and anti drain back valve so you can fit them upside down .
The generic mower filters are all over the web at silly prices, but make sure you get them form some one who only sells mower / motorcycle / car parts and is not a surplus & disposal site as they often sell QC rejects and you don't want to fit one of them .
Other options
1) Honda #15410 MJ0-004 M20 x 1.5 Dia = 3'' length = 3.5"
2) Kawasaki # 16097-1072 M20 x 1.5 Dia = 2.625" length = 2.5"
And there is a nice cross refference site
https://www.oilfilter-crossreference.com/convert/KAWASAKI/16097-1072 so you can find a locally available equivalent.
But note some of them are actually wider & longer because this site uses the size of the threads , the size of the rubber seal & filter rating not the actual diameter of the external can.
They all ship either as individual boxed filters or a bulk pack of 12 for about 2/3 of the single pack price.
As with a lot of things the logistical costs factored into the price are near 1/2 of the retail price.
