HO World

The Magazine For Slot Car Enthusiasts

The International Fray Rules


See individual venue sites for complete rules and formats


Complete Car Regulations:  

1)    The complete car must weigh at or between 20.0 grams and 24.0 grams.

2)    The complete car must freely pass through a standard (1 5/16”) Ho Tech block.


Body Regulations:

1)   The body must be a copy of a 1:1 car and/or concept cars.

2)   Bodies must be manufactured by either the process of casting or injection molding and be made from resin or plastic. No feather light resin allowed.

3)   Bodies with cast in handling pans or exaggerated details (such as unrealistic or inappropriate hood scoops, oversized windows, side pipes, sloped sides, or snow plow noses) are not allowed.

4)   Bodies must be originally manufactured with the intention of being mounted with the use of 2 screws via 2 body mounting posts on a/an: Aurora Model Motoring (which includes: Vibrator, Thunder Jet, Wild Ones, Tough Ones, and Xlerators), Bachmann, Faller, Model Motoring Thunders Plus, Marx Eldon or Tyco S series HO chassis.

5)   No Indy, formula 1 or formula style open wheel bodies will be allowed.

6)   No ballast or fillers, other than color pigment, are allowed in the plastic or resin bodies

7)   Maximum overall body width is 1.200”. Accordingly the body must pass through our 1.2” body tech device.

8)   The maximum thickness of the sides of the body, including items such as fender flares and running boards, is 0.125”

9)   With the body mounted securely to the chassis and viewed from above, the body must cover the chassis except through windows and vents. Unrealistic, overly large windows and vents are not allowed.

10)  With the body mounted securely to rolling chassis and when viewed from the side of the body: The upper edge of the top-plate, minus rail cannot be above the top of the body as measured at the rear of the gear top plate. (i.e.: The horizontal top of the gear plate (base) cannot protrude above the rear window opening)


11) The body must be fitted with the manufacturer’s original or exact replica bumpers, heads, rollover bars, etc. in their stock locations.

12)  Cracked or broken body mounting posts may be repaired or replaced with the use of glue or a plastic sleeve around the original post or a plastic tube in place of the broken post.

13)  Other than the plastic post reinforcements stated in Body Rule 12, no additional weight can be added to the body.

14) The body may be lowered and lightened by removing material through the process of grinding, or scraping, as long as Body Rule 10 is not violated.  Body cannot be heated or reshaped from the original cast of the body.

15)  Bodies that have a separate roof and windshield casting/molding and have molded in interiors (also known as Hardtops, e.g. Aurora’s ’65 Mustang) may have the interior portion of the body completely removed.

16)   Front and rear wheel wells may be opened up for tire wheel-well clearance. This opening may be no larger then 1/8-inch drill bit around entire wheel-well and tire.

17)  Wheel-wells must not be modified in such a way as to allow the use of any other wheelbase that is not originally intended by the manufacture of the body.

18)  Any body mounting screw may be used. Non-magnetic screws are recommended, so a passing car will, not pick up, a loose screw, thus causing damage to the car and/or the track.

19)  Both front and rear screws must be used and must secure the body to the chassis at all times.

20)   The front windshield must be plastic or resin, clear or painted, may be glued in place or molded in, and must fill the window frame. Tape windshields are not allowed. Side and/or rear windows may be removed.



Rolling Chassis Assembly Regulations:

1) Only original Aurora Thunder Jet chassis assemblies with non-plated copper electrical components are allowed.  Brush springs may be bent to alter brush tension.  Pickup shoe hanger plates may be slightly bent.  

2)  The rolling chassis’ axle and armature holes may be slightly opened up for increased clearance. The truck hole cannot be utilized in any way.

3)  The rolling chassis assembly must not be fitted with bushings.

4)  The chassis may be trimmed slightly (no more than .010”) to allow for crown gear tooth clearance.

5)  Any original Aurora T-Jet pancake gray armature with two laminations, with its original commutator, and all of its original unmodified windings may be used.  The armature may be, (balanced, and trued) 

6)  Each armature pole is to be measure across two separate commutator segments. The Average of all three poles must be 16 ohms or greater. I.e. pole A measures @ 15.8 ohms, pole B measures @ 16.2 ohms and pole C measures @ 16.0 ohms – This armature is Legal. All measurements are to be taken at the current available room (ambient) air temperature.  The warming of either the commentator or the armature is not allowed before and during measuring. (The combined total ohm reading of all three armature poles must equal or exceed 48 ohms)

7) Any original Aurora magnets or Johnny lightning magnets must be used. Johnny Lightning magnets may be sanded to fit the chassis. The distance between the magnets must be a minimum of .700; no exaggerated sanding is allowed to close the arm gap. This will be teched using our custom designed, specially fabricated plug.

8)Magnet shims may be used. Shims must be non-ferrous. No shims are allowed either under or on top of magnets.

9) Any flat top and bottom carbon/copper motor brushes are allowed.  Brushes may be scored with one score line or an “X”. No exaggerated deep cuts or crevices allowed. This will be checked at tech.

10) Any stock or commercially available stock replacement 14 tooth brass armature pinion gears are allowed.

11)  Any stock or commercially available stock replacement 24 tooth brass idler and driven gears are allowed.

12) Any stock or commercially available stock replacement 9 tooth brass pinion gears allowed. 

13)  Any stock or commercially available stock replacement 15 tooth crown gears are allowed.  The crown gear boss may be trimmed or a spacer may be added to adjust for proper gear mesh.

14)  Only original Aurora drive gear shaft must be used. The shaft may not be trimmed, cut, or, shortened.

15) Gear tooth friction surfaces may be deburred by polishing, filling or sanding.

16)  Gears may not be chamfered, lightened or relieved.

17)  Any front, rear wheel and, tire, axle may be used, but the front tires cannot be smaller then .300" diameter. Maximum lateral movement in the front wheel assembly is 0.031.

18)  Front and rear axle shim washers or spacers are allowed. Front axel, shim washers or spacers must be on the outside of the frame rails. Refer to Chassis Rule #13 for adding spacers around crown gear.

19)  Any stock or stock replacement pickup shoe must be used. These shoes must have a factory formed step, and the step must be unaltered except to allow flat pickup shoe contact with the track rail. Replacement shoes can be American line shoes #313. Thunder shoes BSRT #504, are allowed. The radius bend on front of the pick-up shoe below the slot may not be altered in anyway.

20) The “ step” in the pick-shoe must remain intact and be unaltered, except that only

the first bend in the step (Bend #2) may be changed slightly so that proper “pick-up shoe “ to” rail” contact can be achieved. NO attempts to “flatten” the “step” are allowed. The area between bend 1 and 2 may “flattened” to achieved better contact with the “rail”. The front, vertical, slotted portion of the pick-up shoe may be bent to limit shoe travel. The rear, hook portion of the pick-up shoe may be bent to limit shoe travel and shoe tension.

21)  The pickup shoe spring may be cut, stretched, shimmed, or compressed.

22)  Any amount of the vertical gear plate rails above the upper horizontal plane may be removed.  No amount of material may be removed from the gear plate at or below the upper horizontal plane. The serial/patent numbers and letters must also remain intact.

23)  Guide pins must be plastic and must be of a design essentially similar to the original Aurora black plastic front guide pins. Guide pin may be, trimmed or bent. Countersinking screw hole on front guide pin is allowed.

24) Glue may be used on a rolling chassis assembly only for the purposes of attaching solid brass gears, guide pin or axles. Solder may be used to attach metal gears to their metal shafts.

Due to the incredible efforts of four individuals, the world finally has a set of Fray International Rules that governing bodies as great as The Fray In Ferndale, and the Quad City Quarrel have accepted.

The importance of this is that the large family of competitors that race this format, can now confidently go to any of the tracks in California, Kansas, Iowa, and throughout the country, and have a car that will be legal in all venues. And this list is growing.

It all started with a major effort from Rick Phillis and Rick Machado, and their child, the Fray, and with the heralded framework of rules designed by Dan Luna and Mike Block, used at there Quad City Quarrel. These men spent uncounted hours in a spirit of compromise and openness to give us clear and concise rules. We thank them for their unselfish effort.

If any groups out there adopts, or is currently using these rules, please let us know so we can add you to the list below.

Venues Using

The International Fray Rules:

1. The Fray in Ferndale
2. Quad City Quarrel