Here is another Linear. Had a place where the cases needed to be stronger so it would push and pull. This linear is capable of much heavier pulls than the 31 (5/16") listed in my things. It uses two 3/8" x 7/8" sealed roller bearings instead of the 12mx18mx4m bearings. With a RS555 or 550 motor this linear will pull 10-20 lbs. If you use a metal backing plate to hold it, will probably do more. Here is a video of the linears working https://www.youtube.com/watch?v=6xfDU2BKSvI&feature=youtu.be Will work with any motor 540-555 with 25mm mounting centers. The motors I am using are Mabuchi RS555PH-23300, 5050 RPM and 380G of tourque, 12-30VDC, 1.25Amp ( available ebay/Parts Express $3.95). You will need a 93 tooth 48P Associated/Arrma type spur gear with the center drilled for the rod and a pinion gear for the motor. Pinion needs to be 12-15 tooth 48P. There is a 93 tooth spur gears you can download and try in the Linear 31 but it won't take much, try adding shells. Also need two 3/8"x7/8"x9/32" sealed bearings, #R6-2RS. Uses 6-32x1" and 3/4" machine screws. Flat heads for inside. Drill the holes to fit. You can use either 1/4-20 or 1/4-28 all threaded rod and nuts, depending on how much speed you need. The nuts are inserted into the gear halves and sandwiches the gear with #4 screws. Using 1/4-28 will pull harder but slower. Threaded rod has to be anchored on the other end of the linear or hold the rod with nuts at gear and use as a jackshaft. Just added all kind of different brackets and nose cones so you can have a variety of mounting options. Mount uses 1/4" bolt. You can also use the linear right through a bulkhead if it is a straight pull. There are screw holes to use 4x3/8 sheet metal screws as bearing retainers if you don't need a bracket or nose cone. Used this linear for the rippers lift motor on my handmade from scratch metal/3D printed 1/6th scale RC Cat D4G Dozer. Linear works great for this application and will push up the back of the dozer that weights 76 lbs. Hope you will find many uses, enjoy!All of the cases and gear halves need to have exterior support to print. The brackets and nose cone should build without support. To assemble the linear you will need to fit the bearing bores so they go in tight. A drum sander on a drill works good for this. Get the bearings in the cases. Make sure gear halves go inside bearing bores okay, file if needed. You will need to drill out the inside of the gear halves for clearance so the rod goes through freely("F", "G" or "H" ). Take the gear halves and insert the nuts in both sides. Sandwich the gear between the halves. Some gears will need holes drilled for the screws. Use 4x1/2 or 3/4" screws to hold gear halves. If stuff doesn't turn straight, turn the halves an 1/4 turn until you get a good matchup and turns straight and mark them so they go back together this way with gear. To get the best results go ahead and screw the rod into the nuts with it all together. Make sure there isn't any play back and forth with the nuts inside. If there is shove the nut farther down in its hole and do again until no/little play, but gear spins freely on rod. To put the linear together mount the case half to whatever side you are mounting to, so you can tighten screws from the inside( use 6-32 or 4m flat head screws and lock nuts if needed). Set the gear in the case and put the other case half over it. Use (4) 6-32 x 1" or 1.25" round head machine screws on the outside to hold cases together. Be sure everything turns freely, switch gear around 180 if hitting screws or file down so turns easy. Install the motor and pinion gear. The motor takes short 3mm button head bolts. Adjust for good gear to gear clearance. If you plan to mount it in a bulkhead or make a metal holder, the cases have a square bolt pattern from a 1.4" diameter circle, so each hole is .7" from the center. The holes are .160" through the case. I used 4mm flatheads from my slash parts with nylock nuts, but 6-32 flatheads will work also. If you find something wrong or needs changes drop me a line.