A downhole rotary drilling tool, comprising: a tool body; an extendible and retractable element associated with the tool body and at least partially projecting from a surface of the tool body; a self-adjusting rate control device coupled to the element, the self-adjusting rate control device configured to cause the element to extend outward relative to the tool body from a retracted position to an extended position at a first rate in the absence of an external force applied to the element, the self-adjusting rate control device including: a piston for applying a force on the element; a biasing member that applies a force on the piston to extend the element; a fluid chamber associated with the piston, wherein the piston sealingly divides the chamber into a first chamber and a second chamber, the first chamber and the second chamber being filled with hydraulic fluid suitable for downhole use, and characterized in that the self-adjusting rate control device is configured to cause the element to retract inward relative to the tool body from the extended position to the retracted position at a second rate different from the first rate in response to external force applied to the element, and wherein the first chamber and the second chamber are in fluid communication with one another via a first fluid flow path having a first fluid control device in the first fluid flow path which is configured to control the rate of flow of the hydraulic fluid from the second chamber to the first chamber, and wherein the first chamber and the second chamber are in fluid communication with one another via a second fluid flow path having a second fluid control device in the second fluid flow path which is configured to control the rate of flow of the hydraulic fluid from the first chamber to the second chamber. a tool body; an extendible and retractable element associated with the tool body and at least partially projecting from a surface of the tool body; a self-adjusting rate control device coupled to the element, the self-adjusting rate control device configured to cause the element to extend outward relative to the tool body from a retracted position to an extended position at a first rate in the absence of an external force applied to the element, the self-adjusting rate control device including: a piston for applying a force on the element; a biasing member that applies a force on the piston to extend the element; a fluid chamber associated with the piston, wherein the piston sealingly divides the chamber into a first chamber and a second chamber, the first chamber and the second chamber being filled with hydraulic fluid suitable for downhole use, and characterized in that the self-adjusting rate control device is configured to cause the element to retract inward relative to the tool body from the extended position to the retracted position at a second rate different from the first rate in response to external force applied to the element, and wherein the first chamber and the second chamber are in fluid communication with one another via a first fluid flow path having a first fluid control device in the first fluid flow path which is configured to control the rate of flow of the hydraulic fluid from the second chamber to the first chamber, and wherein the first chamber and the second chamber are in fluid communication with one another via a second fluid flow path having a second fluid control device in the second fluid flow path which is configured to control the rate of flow of the hydraulic fluid from the first chamber to the second chamber. a piston for applying a force on the element; a biasing member that applies a force on the piston to extend the element; a fluid chamber associated with the piston, wherein the piston sealingly divides the chamber into a first chamber and a second chamber, the first chamber and the second chamber being filled with hydraulic fluid suitable for downhole use, the self-adjusting rate control device is configured to cause the element to retract inward relative to the tool body from the extended position to the retracted position at a second rate different from the first rate in response to external force applied to the element, and wherein the first chamber and the second chamber are in fluid communication with one another via a first fluid flow path having a first fluid control device in the first fluid flow path which is configured to control the rate of flow of the hydraulic fluid from the second chamber to the first chamber, and wherein the first chamber and the second chamber are in fluid communication with one another via a second fluid flow path having a second fluid control device in the second fluid flow path which is configured to control the rate of flow of the hydraulic fluid from the first chamber to the second chamber.