Z Brace| |Stability | | | | "The design allows in a Z axis that can flex and wobble during printing. These modification will make the Z axis very rigid and will improve print quality."| ~$10 | 10 |  | "This kit will add rigidity to your printer, giving you better prints more often."
Guide.Z-Axis Mod | ~$10 | 10 |  | "Remix of AzzA's Z Brace and TyphonPS's design with levelers." Esentially Z Brace with extras
Z Extensions | ~$10 | 7 |  | "This mod compliments the Z Braces and gives the printer an additional 37mm of clearance on the X Crossbeam."
Gantry Feet | Free! | 8 |  | "If you installed your Z-Brace mod you likely noticed your gantry feet no longer touch the surface of where it sits. These fill that gap to provide further stability." | |Cooling | Info | | | "Several options for cooling ducts and shrouds to provide enhanced cooling."
DiiiCooler | ~$8 | 8 |  | "The DiiiCooler is a 360 degree field of cooling around the hotend for the part being printed."
CiiiCooler | ~$8 | 8 |  | Basically the DiiCooler but with a cutout in front so you can see the nozzle, slightly less effective 'Fan Duct' | ~$8 | 7 |  | Very similar design to the CiiiCooler with larger cutout, slightly less effective
Cobra | ~$8 | 8 |  | "The ducts are shaped to deliver a powerful blast from two sides without cooling the hot end too much, and a strong air flow can be felt all around the nozzle." | |Bed | Info | | | Be sure to read reviews to check for warping
RepRap Y Carriage Plate | $25 | 9 |  | "It stops the bed from warping which CONSTANTLY changes your 'bed level' making is so you do not have to tweak your bed level every single print. Once I made that mod alone my bed leveling went to nearly zero." - u/nerys71
Local Store Glass | <$10| 7 |  | You can go to your local hardware store and have them cut you a sheet of Borosilicate glass (if they have it). As other users suggested, you can also get a sheet of normal glass for even cheaper, however be wary as normal glass can shatter after some time from the constant heating and cooling. Should be 8.5"x8"x1/8" to fit best.
RioRand Borosilicate Glass | $20.59 | 7 |  | "After cracking a few sheets of normal glass from rapidly cooling or heating, borosilicate glass will quell your frustrations."
Geeetech Borosilicate Glass | $18 | 7 |  | "Borosilicate glass is rated for higher temperatures than normal sheet glass making it a better material for use as a heated bed." *
Nut Bed Leveling Thumb Wheel | Free! | 7 |  | "Designed specifically for the bed leveling screws. A common mod is to add some M3 nuts to the bed for more stability. A massive improvement when leveling." *
Countersunk Bed Spring Spacer | Free! | 5 |  | Compliments the thumb wheel above. "I noticed the spring would move around on the bottom washer causing uneven pressure and quite imprecise leveling; this spacer will block the spring in a perfectly vertical, flush position making bed leveling an easy and quick business, also gives the adjustment system a more premium look."
Ultem PEI | $8 | 8 |  | Sticks to PLA and ABS and gives a smooth finish. Wipe with isopropyl alcohol once in a while.
Gizmo Dorks PEI Sheet | $16.95 | 8 |  | Sticks to PLA and ABS and gives a smooth finish. Wipe with isopropyl alcohol once in a while.
Glass Bed Corner Clamps | Free! | 7 |  | Adjustable screw clamps to hold your glass bed in place. Printing this with PLA is not recommended.
Blue (Painter's) Tape | $4.99 | 6 |  | If you don't want to use pads or something else to hold it in place, you can just tape down the corners of the glass. | Heat Transfer | Info | |  | Transfer the heat from the plate the glass. "You don’t have to cover the whole surface with the thermal pad. Cutting it into 2" squares and placing them in the corners and the middle work just fine."
ARCTIC Thermal Pad | $15 | 8 |  | Branded, has great reviews. | *Extruder Gear | Info | | | "Replacing the gear will improve print quality and may help reduce skipping and clogs with its firm grip on the filament." *3DP2GO | $3.50 | 5 |  | "38 Teeth steel extruder drive gear ID 5mm" *
Micro Swiss MK10 All Metal Hotend 0.6mm | $37.75 | 7 |  | "All metal hotend will let you print at much higher temperature then possible with original PTFE lined one. Another benefit of an all metal hotend design is more consistent melt chamber control."
RADDS | $63 | 2 |  | "32 bit Processor, removable stepper drivers, full size SD card and a whole lot of extra features."
Guide.RAMPS | ~$65 | 2 |  | "8bit Processor, removable stepper drivers and other nice features." Guide. | Other | | | | Items which don't fit in the categories above but may be useful290pcs M3 Phillips Screws Bolts Nuts Washers | $11.99 | - |  | Required for many mods. There's a lot of different packs so get however many you need.
Bed Heater Cable Protector | Free! | 3 |  | "The bed heater cable would snag on a metal tab on the base as the print bed moved back and forth. This part slips over the tab and provides a smooth sloped surface for the cable to slide over - preventing the cable from catching."
Simple Belt Tensioner | Free! | 3 |  | "Using this you can have easy-install and easy-tighten belts without the issues caused by the built-in spring tensioners."
LM8UU Bearings | $10.99 | 3 |  | These can replace the y-axis bearings that tend to have issues. Any quality LM8UU bearings you find will do. *May already be upgraded on newer models