A covering for an architectural opening, comprising: a head rail; a covering for an architectural opening extending from said head rail, said covering being extendable from and retractable toward said head rail; a first shaft (1022', 1024') mounted in said head rail for rotation in clockwise and counterclockwise directions about a first axis of rotation, said first shaft (1022', 1024') having a non-cylindrical profile and being operatively connected to said covering for extending and retracting said covering as the first shaft (1022', 1024') rotates; and a first limiter (1025'M, 1025'B, 1040) operatively connected to said first shaft (1022', 1024') to stop the rotation of said first shaft (1022', 1024') upon extending the covering a desired distance, said first limiter (1025'M, 1025'B, 1040) including: a base (204, 1042) fixed relative to the head rail, said base (204, 1042) defining a first set of threads (230,1044, 1046) and a first axially extending shoulder (210, 1064); a first hollow rod (206, 1068) defining a second set of threads which are engaged with said first set of threads (230, 1044, 1046), wherein said first shaft (1022', 1024') extends through said first hollow rod (206, 1068) and the first hollow rod (206, 1068) and first shaft (1022', 1024') define mating profiles that cause the first hollow rod (206, 1068) to rotate with the first shaft (1022', 1024') while allowing the first hollow rod (206, 1068) to slide axially relative to the first shaft (1022', 1024'); characterized in that said first hollow rod (206, 1068) defines a second axially-projecting shoulder (1076, 1078), wherein, as said first shaft (1022', 1024') rotates in a first direction, it causes the first hollow rod (206, 1068) to rotate relative to the base (204, 1043), with the engaged threads causing the first hollow rod (206, 1068) to slide axially relative to the first shaft (1022', 1024') until the first and second axially-projecting shoulders abut each other, thereby stopping rotation of the first shaft (1022', 1024') in the first direction. a head rail; a covering for an architectural opening extending from said head rail, said covering being extendable from and retractable toward said head rail; a first shaft (1022', 1024') mounted in said head rail for rotation in clockwise and counterclockwise directions about a first axis of rotation, said first shaft (1022', 1024') having a non-cylindrical profile and being operatively connected to said covering for extending and retracting said covering as the first shaft (1022', 1024') rotates; and a first limiter (1025'M, 1025'B, 1040) operatively connected to said first shaft (1022', 1024') to stop the rotation of said first shaft (1022', 1024') upon extending the covering a desired distance, said first limiter (1025'M, 1025'B, 1040) including: a base (204, 1042) fixed relative to the head rail, said base (204, 1042) defining a first set of threads (230,1044, 1046) and a first axially extending shoulder (210, 1064); a first hollow rod (206, 1068) defining a second set of threads which are engaged with said first set of threads (230, 1044, 1046), wherein said first shaft (1022', 1024') extends through said first hollow rod (206, 1068) and the first hollow rod (206, 1068) and first shaft (1022', 1024') define mating profiles that cause the first hollow rod (206, 1068) to rotate with the first shaft (1022', 1024') while allowing the first hollow rod (206, 1068) to slide axially relative to the first shaft (1022', 1024'); characterized in that said first hollow rod (206, 1068) defines a second axially-projecting shoulder (1076, 1078), wherein, as said first shaft (1022', 1024') rotates in a first direction, it causes the first hollow rod (206, 1068) to rotate relative to the base (204, 1043), with the engaged threads causing the first hollow rod (206, 1068) to slide axially relative to the first shaft (1022', 1024') until the first and second axially-projecting shoulders abut each other, thereby stopping rotation of the first shaft (1022', 1024') in the first direction. a base (204, 1042) fixed relative to the head rail, said base (204, 1042) defining a first set of threads (230,1044, 1046) and a first axially extending shoulder (210, 1064); a first hollow rod (206, 1068) defining a second set of threads which are engaged with said first set of threads (230, 1044, 1046), wherein said first shaft (1022', 1024') extends through said first hollow rod (206, 1068) and the first hollow rod (206, 1068) and first shaft (1022', 1024') define mating profiles that cause the first hollow rod (206, 1068) to rotate with the first shaft (1022', 1024') while allowing the first hollow rod (206, 1068) to slide axially relative to the first shaft (1022', 1024'); characterized in that said first hollow rod (206, 1068) defines a second axially-projecting shoulder (1076, 1078), wherein, as said first shaft (1022', 1024') rotates in a first direction, it causes the first hollow rod (206, 1068) to rotate relative to the base (204, 1043), with the engaged threads causing the first hollow rod (206, 1068) to slide axially relative to the first shaft (1022', 1024') until the first and second axially-projecting shoulders abut each other, thereby stopping rotation of the first shaft (1022', 1024') in the first direction.