CW there is a difference in the 404 and 405 it is the impellor blade some have a straight shaped blade and some have a curved shaped blade make sure you look at the type you have before you order a replacement.
Please call me Gunner, my friends do. If you look on ebay for Fluval 405 impeller they say "404/405 strait blade", so the curve must be new, wonder if it fits lol. The funny part is that according to both manuals the pump output are identical 1300L or 340G and so are all the other specs on the table right down to the wattage on the motors, a prime indicator of power. Also if you go to the hagen website and look up the manuals in PDF on the parts list both "magnetic impeller" part numbers are identical A-20172. So whether curved or strait must be interchangable, also the exspoded parts list shows is labled 404/405 almost all parts interchnagable, just like when Hagen AquaCleal chnaged the names of the ACs from 500/110 300/70 exc, I think it was just a marketing ploy.
Fluval 404/405 Parts (Pet Solutions)
Item No. Description Stock Qty Price
15511217 SUCTION CUP BRACKET
15515041 SUCTION CUPS FOR BRACKET 4PK
15520000 DIRECTIONAL OUTPUT NOZZLE Item expected in on 8/3/2009
15520005 INTAKE STEM
15520007 INTAKE STRAINER W/CHECK BALL
15520015 RIBBED HOSING FOR 304 & 404
15520017 RUBBER ADAPTER FOR RIBBED HOSINGv304 & 404 Item expected in on 8/3/2009
15520019 HOSE ELBOW FOR RIBBED HOSING 304 &v404
15520020 SELF PRIMER ASSEMBLY
15520058 HOSE LOCK NUT
15520060 AQUA-STOP FEATURE
15520063 MOTOR SEAL RING
15520066 CERAMIC SHAFT & RUBBER SUPPORT - New Style
15530170 MAGNETIC IMPELLER FOR 404 - OLD STYLE
15530172 MAGNETIC IMPELLER FOR 404/405 - NEW STYLE
15520067 BIOLOG. MEDIA COVER 304 & 404
15520070 MEDIA CHAMBER 304 & 404
15520119 RUBBER FEET
15520177 FOAM INSERT ASSBLY FOR 404
15530156 IMPELLER COVER 304 & 404 - NEW STYLE
15530174 IMPELLER WELL/ INSERT 304/404
15520160 MOTOR HEAD
15530197 FILTER CASE FOR 404 - New Style
15530022 FLUVAL CANISTER CLIP