DENSO(JAPAN) has started to supply 5 kinds of 0.7mm long life Iridium Plug to Honda Civic since January 2006.
They are SK20HPR-L11, SK20PR-L11, SKJ20DR-M11S, SKJ20DR-M11 and SK22PR-M11S. These plugs are called longlife Iridium Plugs which DENSO developed in 1997 and possesses around 50 patents all over the world. DENSO Iridium alloy consists of Iridium and Rhodium. And DENSO was awarded by SAE, Arch T Colwell for this new technology.
As Civic have various displacement and vehicle type, DENSO supplies 5 kind of Iridium plugs for their variations. The specification of the plugs is in the table 1. DENSO also recommends aftermarket Iridium Power and Iridium Tough accordingly shown in table2.

[SKJ20DR-M11S] Click to enlarge

[SK22PR-M11S] Click to enlarge

[SK20HPR-L11] Click to enlarge

TABLE1:2006 CIVIC DENSO SPARK PLUG CHART

Vehicle	Veicle Code	Displacement(cc)	JAPAN	NorthAmerica	China	Other Area
CIVIC HYBRID	IMA	1300	SK20HPR-L11	SK20HPR-L11	-	-
CIVIC	NP1	1400	-	-	-	SK20PR-L11
CIVIC	NP4	1600	-	-	-	SKJ20DR-M11S
CIVIC	NP4	1800	-	SKJ20DR-M11S	-	SKJ20DR-M11S
CIVIC	ExceptNP4	1800	SKJ20DR-M11S	SKJ20DR-M11S	SKJ20DR-M11S	SKJ20DR-M11S
CIVIC	NP2	2000Si	-	SK22PR-M11S	-	-
CIVIC(Acura)	NP2	2000	-	SKJ20DR-M11	-	-

TABLE2:Spark plug adaptaion chart from Denso to Iridium Power/Tough

DENSO TYPE	Honda P/N	Spec.	Japan,USA & Europe		Asia
			Iridium Power	Iridium Tough	Iridium Power	Iridium Tough
SK20HPR-L11	12290-RMX-004	Iridium Longlife(26.5mm Reach)	IKH20	VKH20	IKH20	VKH20
SK20PR-L11	98079-5615V	Iridium Longlife	IK20	VK20	IK20	VK20
SKJ20DR-M11S	9807B-561CW	Iridium Longlife with SUS gasket	IK20G	VK20G	-	-
SKJ20DR-M11	9807B-5615W	Iridium Longlife	IK20	VK20	IK20L	-
SK22PR-M11S	98079-571CV	Iridium Longlife with SUS gasket	IK22G	VK22G	IK22G	VK22G