Md. Code Regs. 11.13.08.10 – Tables.

A. Table 1. Figure 1.—TYPICAL COUPLER AND BALL TEST FIXTURE ARRANGEMENT

LIGHT SERVICE DEVICES BREAKING STRENGTH FOR COUPLINGS AND BALLS
Trailer Classification	Trailer Couplings Designation	Minimum Ball Diameter-Inches (Where Ball-Type hitch is used)	Minimum Breaking Point Requirements	Pounds
Class 1 (2,000 lbs. or less MGTW)	No. 1	1-7/8	Longitudinal tension:	6,000
			Longitudinal Compression:	6,000
			Transverse thrust:	2,000
			Vertical tension	2,500
			Vertical compression:	2,500
Class 2 (2,001 thru 3,500 lbs. MGTW)	No. 2	2	Longitudinal tension:	10,500
			Longitudinal compression:	10,500
			Transverse thrust:	3,000
			Vertical tension:	4,500
			Vertical compression:	4,500
Class 3 (3,501 thru 5,000 lbs. MGTW)	No. 3	2	Longitudinal tension:	15,000
			Longitudinal compression:	15,000
			Transverse thrust:	4,000
			Vertical tension:	7,000
			Vertical compression:	7,000
Class 4 (5,001 thru 10,000 lbs. MGTW)	No. 4	Ball & Bolt shall be of such size and strength as to conform to the minimum breaking strength requirements of the mating coupling required for the specific load of Class 4 trailer.	Longitudinal tension: MGTW x 3 Longitudinal compression: MGTW x 3 Transverse thrust: MGTW x 1 Vertical tension: MGTW x 1.3 Vertical compression: MGTW x 1.4

Typical coupler and ball test fixture arrangement diagram. "Note: Test fixture bars to be solid and fit snugly inside of housing channels."

B. Table 2. V = Vertical Force (lbs.) L = Longitudinal Force (lbs.) T = Transverse Force (lbs.) M = Spring Bar Moment (inch-lbs.) R = Hitch Rating in Terms of MGTW (lbs.) (Maximum Gross Trailer Weight) X = Hitch Rating for Maximum Vertical Load on Hitch (lbs.) (Tongue Weight) Figure 2 * Footnotes to Table 2 and Figure 2.

(a) When a hitch is to be tested:
1. (1) Assemble the hitch in its normal configuration as recommended by the hitch manufacturer.
2. (2) Attach the hitch to a non-yielding restraining fixture. The hitch-to-fixture attaching means shall be the same as the normal hitch-to-car attaching means recommended by the hitch manufacturer.
3. (3) The points of hitch-to-fixture attachment shall be located in the same positions as the hitch-to-car attachment point locations recommended by the manufacturer.
4. (4) Attach a ball to the ball support platform in the manner recommended by the hitch manufacturer.
(b) Hitch Test Force Applications. With the hitch attached to the test fixture as specified in footnote(a), above, successively apply the forces designated in Table 2, as follows:
1. (1) Apply the specified downward vertical force concurrently with the specified compressive longitudinal force or spring bar moment.
2. (2) Apply the specified tensile longitudinal force concurrently with the specified downward vertical force.
3. (3) Apply the specified compressive longitudinal force concurrently with the specified downward vertical force.
4. (4) Apply the specified leftward transverse force.
5. (5) Apply the specified rightward transverse force.
6. (6) For hitches with weight distributing capability, apply the specified spring bar, or leveling moment, concurrently with the specified downward vertical force. All forces in steps(1) through (6) are to be applied along an axis which intersects the center of the ball. All forces are to be applied with an onset rate of not more than 150 pounds per second, and maintained at the maximum specified force level for at least 5 seconds.
(c) Each hitch, when tested as specified above, shall be capable of withstanding the forces applied in accordance with footnote (b), immediately above, without causing permanent deformation of the ball platform, such that the final position of the ball axis may not depart more than 5 degrees from its original, nominally vertical position.

HITCH TEST FORCES*
STEP	WEIGHT CARRYING HITCH		WEIGHT DISTRIBUTING HITCH
Force	Direction	Force	Direction
1. V= .47R + 480	Downward	V = .045R + 1650	Downward
L = .47R + 480	Compressive	M = 51,000	See Figure 2
2. L = .23R + 1530	Tensile	L = .067R + 2070	Tensile
V = .15R	Downward	V = .15R	Downward
3. L = .23R + 1530	Compressive	L = .067R + 2070	Compressive
V = .15R	Downward	V = .15R	Downward
4. T = .20R + 500	Leftward	T = .20R + 500	Leftward
5. T = .20R + 500	Rightward	T = .20R + 500	Rightward
6. Not applicable	Not applicable	M = 93.2X + 21000	See Figure 2
		V = .15R	Downward

Car hitch diagram explaining various force directions.

C. Table 3. *Maximum Gross Trailer Weight

MAXIMUM RECOMMENDED TONGUE WEIGHTS BY TRAILER CLASSIFICATION FOR TRAILER DESIGN
Class Trailer	Maximum Gross Trailer Weight (MGTW, lb.)	Maximum Static Tongue Loads, Lb.	Recommended Type of Hitch
1	Up to 2000	200	Weight carrying hitch
		300	Weight distributing hitch
2	2000 to 3500	300	Weight carrying hitch
		500	Weight distributing hitch
3	3500 to 5000	15% MGTW*	Weight distributing hitch
4	5000 to 10,000	15% MGTW*	Weight distributing hitch

D. Table 4. * Load shown shall be applied in the same manner as would prevail if the trailer were being towed by the safety chain in a straight ahead direction. Safety chain, when formed, fastened, or rigged as on the vehicles, shall withstand load shown without breaking. Local marking, denting, or gouging of the chain attaching means at the points of safety chain contact is not considered excessive distortion. The intent is that the chain attaching means shall have sufficient strength to break the safety chain consistently. ** “MGTW” means the maximum gross trailer weight, pounds, which is to be towed.

LIGHT SERVICE DEVICES—MINIMUM STRENGTHS OF SAFETY CHAINS AND ATTACHING MEANS*
Trailer Classification	Minimum Longitudinal Load, Tension, Pounds (See Figures 2 and 3)
Trailer Classification	Each Safety Chain	Each of Two Chain Attaching Means
Class 1	2,000	2,000
Class 2	3,500	3,500
Class 3	5,000	5,000
Class 4**	MGTW	MGTW

E. Table 5. Figures 3 & 4. TYPICAL SAFETY CHAIN INSTALLATION

Authority: Transportation Article, §§12-104(b) and 24-107, Annotated Code of Maryland

Effective date: January 1, 1974

Regulation .01 repealed effective June 17, 1996 (23:12 Md. R. 871)

Regulation .03 amended effective June 17, 1996 (23:12 Md. R. 871)

Regulation .03B amended effective October 27, 2014 (41:21 Md. R. 1260)

Regulation .07A amended effective June 17, 1996 (23:12 Md. R. 871); October 27, 2014 (41:21 Md. R. 1260)

Regulation .08A amended effective October 27, 2014 (41:21 Md. R. 1260)

Regulation .09 amended effective June 17, 1996 (23:12 Md. R. 871)

Regulation .09 repealed effective October 27, 2014 (41:21 Md. R. 1260)

Regulation .10A amended effective October 27, 2014 (41:21 Md. R. 1260)

Regulation .11 repealed effective June 17, 1996 (23:12 Md. R. 871)